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1
Garratt, Patrick Ashworth. "Comparative aspects of the reproductive biology of seabreams (Pisces: Sparidae)." Thesis, Rhodes University, 1994. http://hdl.handle.net/10962/d1005088.
Abstract:
Sexuality in seabreams (Sparidae) is considered to be more complex than in any other family of fishes. Early work indicated five reproductive styles within the family: protandry, protogyny, simultaneous hermaphroditism, rudimentary hermaphroditism and gonochorism. More recently two reproductive styles have been suggested: sex change (protandry and protogyny) and secondary gonochorism (rudimentary hermaphrodites). The need for detailed descriptions of sex differentiation, gonad development and spawning behaviour in this family has been identified by a number of workers in this field. The aims of the present study were: i) to provide accurate, detailed descriptions and comparisons of gonadal development in representatives of each reproductive style, ii) to investigate their spawning strategies, and iii) to relate these findings to current theories on hermaphroditism and sex change in fishes. Four species were investigated. Slinger, Chrysoblephus puniceus, the only known protogynous hermaphrodite in Natal. Santer, Cheimerius nufar, described in the literature as a rudimentary hermaphrodite. Riverbream, Acanthopagrus berda suspected to be a protandrous hermaphrodite. Natal stump nose, Rhabdosargus sarba, reported elsewhere as a protandrous hermaphrodite. Detailed histological analysis showed that morphological and cytological development of all gonads proceeded initially in a female direction, irrespective of reproductive style, but that differentiating gonads of protandrous and protogynous hermaphrodites could easily be distinguished from one another. Early gonadal development was similar in R. sarba and A. berda with gonadal primordia differentiating into distinctly bisexual organs. In C. puniceus and C. nufar gonadal primordia differentiated into ovaries with reduced, inert male elements in the tunica albuginea. Sex differentiation occurred relatively late (100-150mm fork length) in all the species investigated. Few cells conforming to primordial germ cells (PGC's) described in other teleosts were identified. These cells only became evident after the appearance of gonial cells and their identity is questioned. Gonial cells appeared to develop within less-electron-dense cysts of cells. Gonial cells in presumptive male and female elements could not be distinguished from one another morphologically, suggesting the bipotentiality of these cells. All R. sarba and A. berda gonads pass through a predominantly male phase and all fish function first as males, indicating protandrous sex change in both species. All C. puniceus and C. nufar gonads develop initially into ovaries. Sex change thus occurs in both species and protogyny in C. puniceus is confirmed. In C. nufar, sex change may occur before or after sexual maturity and its reproductive style remains uncertain. Investigations into the spawning habits of A. berda have shown that this species spawns inside the Kosi estuary at night. Eggs are released during peak ebb tides. Spawning occurs in large aggregations and several to many males compete to spawn with individual females. This spawning strategy does not conform to predictions made from the size advantage model for protandrous species. Chrysoblephus puniceus appears to have preferential spawning sites on down-current outer reef margins. Spawning was not observed in this species, but changes in behaviour, social structure and colour during the spawning season suggest that it may have a mating system similar to several protogynous labrids and scarids, in which territories are temporary. Cheimerius nufar has a similar mating system. Temporary territories are established by large males during the spawning season, which extends from August to November. Mating is by pair-spawning and dominant territorial males obtain a disproportionate number of matings. 'Streaking' appears to represent an alternative mating strategy for males until they attain a sufficient size to establish and defend territories. The mating pattern of C. nufar suggests that it is either a gonochorist which does not conform to current theoretical predictions; or that it is a protogynous hermaphrodite incorrectly diagnosed as a rudimentary hermaphrodite; or that protogyny in the Sparidae is an ancestral condition and C. nufar is in the process of evolutionary change from a protogynous to a gonochoristic form (or visa versa).
2
Wakefield, Corey Brion. "Latitudinal and temporal comparisons of the reproductive biology and growth of snapper, Pagrus auratus (Sparidae), in Western Australia." Wakefield, Corey Brion (2006) Latitudinal and temporal comparisons of the reproductive biology and growth of snapper, Pagrus auratus (Sparidae), in Western Australia. PhD thesis, Murdoch University, 2006. http://researchrepository.murdoch.edu.au/382/.
Abstract:
This study focused on obtaining sound quantitative data on the reproductive biology, length and age compositions and growth of the snapper Pagrus auratus in the waters off Carnarvon at ca 25oS and Perth at ca 32oS on the west coast of Australia and at ca 34oS on the south coast of Western Australia. Sampling thus encompassed both sub-tropical and temperate waters and the geographical range within which this species is abundant in Western Australia. The resultant data were used to explore the ways in which the biological characteristics of P. auratus differ with latitude and thus water temperature. An intensive sampling regime for eggs and spawning individuals of P. auratus was conducted in Cockburn Sound, a large marine embayment in the Perth region at ca 32oS. The resultant data were used to elucidate where and when spawning occurs in this large marine embayment and to determine more precisely the factors that influence the timing of spawning. The implications of the results presented in this thesis for the management of P. auratus, a species that has been subjected to very heavy fishing pressure in recent years, are discussed.
The time and duration of spawning of P. auratus in the subtropical waters of Carnarvon differed markedly from those recorded for this sparid in the temperate and cooler waters of the Perth and the south coast regions. Spawning at Carnarvon occurred predominantly in the five months between late autumn (May) and mid spring (September), whereas it took place mainly in the three months between mid spring (October) and early summer (December) in the Perth region. Spawning of P. auratus on the south coast occurred predominantly in October and November in 2003 and 2004 and scarcely at all in 2005. Gonadal recrudescence was thus initiated when water temperatures were close to their maximum but declining in Carnarvon, and close to their minima and rising in the Perth and south coast regions, respectively. The prevalence of fully mature and spawning females in all three regions was greatest in those months when water temperatures lay between 19 and 21oC. Collation of the data in this thesis and those provided in the literature for other populations showed that the spawning period was related to latitude, occurring far earlier in sub-tropical than temperate waters.
The females and males attained maturity at a far smaller total length (L50) in the Carnarvon region, i.e. 378 and 353 mm, respectively, than in the Perth region, 585 and 566 mm, respectively, and also the south coast region, i.e. 600 and 586 mm. The trends exhibited by the age at maturity parallel those for length, with the A50s for the two sexes increasing from ca 4 years in Carnarvon to ca 5.6 years in the Perth region and nearly 7 years in the south coast region. The L50 and A50 at maturity thus both increased with increasing latitude.
Marginal increment analysis demonstrated that, irrespective of the number of opaque zones in the otoliths of P. auratus, a single such opaque zone is laid down each year in these otoliths. Furthermore, the trends exhibited by the monthly marginal increments showed that the opaque zone is laid down predominantly in winter in the subtropical waters of Carnarvon, as opposed to mainly in spring in the temperate waters of the Perth and south coast regions. Thus, the timing of formation of the opaque zone in the otoliths of P. auratus along the Western Australian coast is not related to the trends exhibited by water temperature, but, in both the Carnvarvon and Perth regions, was coincident with the timing of spawning.
The maximum total lengths recorded for females and males in the Carnarvon region, i.e. 864 and 840 mm, respectively, were considerably less than the corresponding values of 1051 and 1056 mm in the Perth region, and 1083 and 1099 mm in the south coast region. Growth in the Perth and south coast regions was greater than in Carnarvon, as is reflected in, for example, the respective lengths of 820, 720 and 610 mm for females at 10 years of age, as determined from the von Bertalanffy growth equations.
The length and age compositions in the Carnarvon and south coast regions were essentially unimodal, whereas those in the Perth region were bimodal. However, the 'mode' in the length-frequency distribution for the south coast region was located well to the right of that in the Carnarvon region, reflecting relatively lower contributions by individuals of the age cohorts of 3 to 6 years. The marked bimodality in the length-frequency distribution for P. auratus in the Perth region was due to the presence of a group of mainly smaller individuals caught outside Cockburn Sound and another of mainly larger individuals that were caught in Cockburn Sound and which formed part of a spawning aggregation in that embayment.
The proportion of fish > 10 years old in the Carnarvon region declined markedly between 2003 and the following two years, presumably reflecting the effect of heavy fishing pressure. This contributed to the decision by fisheries managers to reduced the TAC in those waters after 2003. Age-frequency data demonstrated that annual recruitment success in Cockburn Sound varied greatly, with the 1991, 1992 and 1996 year classes being particularly strong, and recognizing that the relative numbers of the first two year classes did decline progressively between 2002 and 2004. Annual recruitment was particularly variable in the south coast region, with the catches of the 1996 year class dominating the samples.
The relative number of early stage P. auratus eggs in ichthyoplankton samples collected from Cockburn sound on each of four new moons during the spawning seasons of four consecutive years peaked in November in three of those years, i.e. 2001, 2003 and 2004, and in November/December in the remaining year, i.e. 2002. This showed that spawning in this embayment peaked during these months, at which times the mean sea surface temperatures ranged only from 19 to 20oC.
The prevalence of spawning fraction females in sequential samples demonstrated that spawning peaks at the new and, to a lesser extent, full moons. This helps account for the strong positive correlation between spawning fraction and tidal regime, with spawning being greatest when the tidal range is greatest.
Spawning times, back-calculated from the ages of the eggs collected during ichthyoplankton surveys in Cockburn Sound on each of 16 new moons within the spawning periods of four successive years, demonstrated that, in this embayment, P. auratus spawns at night and within the first three hours of the onset of the ebb tide. The distribution of egg concentrations on the 16 new moons showed that, each year, spawning occurred firstly in the north-eastern area of Cockburn Sound and then in the middle and finally north-western areas of this embayment.
In the Perth region, the marine embayments of Cockburn and Warnbro Sound act as nursery areas for P. auratus during the first two years of life. The majority of 2 to 5 year old fish and a large proportion of the 6 year old fish occupy the marine waters outside the embayments. The remaining 6 year old and almost all of the older fish begin to move in September into particularly Cockburn Sound, where they form relatively large spawning aggregations between October and December, before undergoing a massive emigration from this embayment in December/January. The limited returns from fish that were tagged in Cockburn Sound and were subsequently caught outside this embayment indicate that, following spawning, P. auratus does not tend to move in a particular direction.
Pagrus auratus stocks are heavily exploited in offshore, oceanic waters and in embayments, such as Cockburn Sound, where they are particularly susceptible to capture because of the tendency of this species to form spawning aggregations in these same easily accessible locations each year. The data obtained during this thesis show that the L50 at maturity of females and males in temperate waters, i.e. nearly 600 mm, is far greater than the current minimum legal length (MLL) of 410 mm TL. There is thus a need to increase the MLL and/or reduce fishing pressure on immature individuals in open waters. However, the effectiveness of an increase in the MLL may be limited because there is evidence that P. auratus suffers from fishing-induced barotrauma. Closures of specific areas during the spawning season of P. auratus, such as those that have been applied in Cockburn Sound and Shark Bay, are potentially a very effective method for reducing the effects of heavy fishing on spawning individuals.
3
Davis, Jerome Adam. "Investigations into the larval rearing of two South African sparid species." Thesis, Rhodes University, 1997. http://hdl.handle.net/10962/d1005138.
Abstract:
The most significant bottleneck to the development of marine finfish culture is a reliable production of juveniles for growout. This is due to the small size at hatch and delicate nature of the pelagic larvae produced by most commercially desirable species. However, over the last 30 years, improved larviculture techniques have been developed to the extent that many species are being successfully cultured worldwide. These techniques were applied to two endemic species as a preliminary step towards establishing marine finfish aquaculture in South Africa. Adult roman Chtysoblephus laticeps and carpenter Argyrozona argyrozona (Pisces: Sparidae) were caught in the Tsitsikamma National Park. Both species responded to injection with pituitary extract, HCG and LHRHa, and were succesfully stripped up to 48 hours after injection. Fish were stripped twice, the second stripping producing better quality eggs. Chyrysoblephus laticeps also spawned naturally after injection with LHRHa. The fertilised eggs were incubated and the larvae reared in a fully recirculating seawater system. One batch of A. argyrozona and three batches of C. laticeps were reared through metamorphosis on a diet of enriched rotifers and Anemia, and inert foods, following commonly used rearing procedures. Both species followed developmental patterns of other cultured larvae, displaying typical critical stages; high mortalities at first-feeding and cannibalism from 26-30 days after hatch resulted in survival rates ranging from 0.1-0.5%. Growth, survival, size of gape at first-feeding, and ease of weaning onto an inert diet of C. laticeps was comparable to other species being reared for the first time, indicating some potential as a candidate species. The numbers of A. argyrozona larvae reared were insufficient to make comparisons with other studies. The adults also proved to be susceptible to physical damage while in captivity and were, therefore, considered unsuitable for aquaculture. The thesis describes the spawning procedure, the systems developed and the larval rearing process. The critical stages of first-feeding, swim bladder inflation, settlement and cannibalism are discussed and the development of the larvae described. The ontogeny of both species is described in detail. Both species displayed typical sparid developmental patterns, but differed with respect to pigmentation, head spination and morphometrics.
4
Mann, Bruce Quintin. "Aspects of the biology of two inshore sparid fishes (Diplodus sargus capensis and Diplodus cervinus hottentotus) off the south-east coast of South Africa." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1005065.
Abstract:
The blacktail, Diplodus sargus capensis and the zebra, Diplodus cervinus hottentotus, sparid fishes endemic to South Africa, are important components of the recreational shore-fishery. To provide a basis for the management of these fish, aspects of the biology of both species were investigated in the Tsitsikamma National Park (TNP). In particular, the role of the TNP was evaluated as a management option for the conservation of both species. Examination of stomach contents showed that juveniles of both species fed predominantly on amphipods, polychaetes and harpacticoid copepods. Adult !h. sargus were omnivorous and fed opportunistically on a wide variety of reef associated invertebrates and algae including echinoids, polychaetes, anthozoans, ascidians and rhodophytes. The diet of adult D. cervinus was more specialized with a preference shown for polychaetes and amphipods. Seasonal differences were apparent in the diets of both species where considerably more amphipods were consumed in winter than in summer. Feeding requirements of both species were reflected in their habitat preferences. Visual underwater assessment revealed that both species were most abundant on turbulent inshore reefs (1-10m). !h. sargus were observed over a wide variety of reef associated habitats. In the literature they have also been recorded in the surf zone of sandy beaches and in the lower reaches of estuaries. !h. cervinus, on the other hand, were more specific in their habitat requirements and were observed in greatest abundance on inshore reefs, often in close association with caves or overhangs. A comparison between the relative abundance and size structure of both species in the TNP with that of an exploited area immediately adjacent to the reserve, showed no significant differences. This was attributed to the low level of exploitation by rock-and-surf anglers occurring in the exploited study area, as well as the possibility of seeding of eggs and larvae, or emigration of adults from the TNP. An investigation of the reproductive biology of both fish showed that !h. sargus had an extended summer spawning season while in !h. cervi nus it was more restricted. Detailed histological examination of gonadal development showed that !h. sarqus were dygynous with partial protandry occuring in the male population. ~ cervinus were shown to be rudimentary hermaphrodites. Size at 50% maturity in ~ sargus and ~ cervinus was determined at 225 and 285mm fork length respectively, corresponding to ages of 4 and 6 years. An age and growth study based on the examination of sectioned otoliths showed that both species were slow growing capable of reaching ages in excess of 20 years. Growth in ~ sargus and ~ cervinus was described by the von Bertalanffy growth equations: L(t) = 309.44(1-e-0 . 247[t+l. 048 l) and L(t) = 396.85(1-e-0.146[t+2.148J) respectively. Life history characteristics of D. sargus and D. cervinus including slow growth, late maturation and occupation of a localised, demersal habitat showed that both species were vulnerable to the effects of over-fishing. Due to the present increase in the number of participants and the decrease in catch per unit effort in the recreational shore-fishery, more stringent management recommendations were proposed to ensure the adequate protection of both species. These included an increased minimum size limit and a decreased bag limit for both species. Based on the residency shown by both species and their high relative abundance in the TNP, marine reserves were considered to be a valuable addition to the suite of management options available for the conservation of these species . In this respect the reserve provided both protection for the spawner stock as well as the potential to seed adjacent areas.
5
Orrell, Thomas M. "A molecular phylogeny of the Sparidae (Perciformes: Percoidei)." W&M ScholarWorks, 2000. http://web.vims.edu/library/Theses/Orrell2000.pdf.
6
González, González Patricia. "Parasitofauna branquial de Dentex dentex (Linneo, 1758) (Pisces: Sparidae)." Doctoral thesis, Universitat de València, 2005. http://hdl.handle.net/10803/10345.
Abstract:
Se ha llevado a cabo un estudio sobre el parasitismo branquial de 91 dentones (Dentex dentex, Pisces, Sparidae). Dicha muestra se compuso de 61 dentones salvajes capturados mediante palangre procedentes de aguas de Mallorca y canal de Menorca, y 30 dentones cautivos procedentes de una jaula situada en el puerto de Mallorca. Se encontraron un total de ocho especies parásitas, un dinoflagélido (Amyllodinium ocellatum), un monogénido (Microcotyle erythrini), un udonélido (Udonella caligorum), un trematodo digenea (Stephanostomum sp. metacercariae), tres copépodos (Caligus productus, Caligus diaphanus y Clavellotis fallax) y un isópodo (Gnathia vorax, praniza larvae). De dichas especies únicamente el dinoflagélido apareció en la muestra de peces cautivos, hallándose el resto de parásitos encontrados en la muestra de peces salvajes. El udonélido Udonella caligorum fue hallado como hiperparásito o foronte de los tres copépodos. Se describen, las prevalencias, intensidades y abundancias medias, así como otros parámetros ecológicos, igualmente se estudia la distribución espacial de cada parásito sobre el tejido branquial. Se discute el hipotético daño que las infecciones producidas por estos parásitos podrían causar en peces cultivados en el área de estudio. No se han podido establecer correlaciones positivas entre los diferentes parásitos y las condiciones de peso/talla del hospedador, no pudiendo concluir por lo tanto, que el número de parásitos aumente según lo hace el tamaño del hospedador. Sólo aparecieron correlaciones positivas entre los cáligos y C. diaphanus y C. fallax. Al ordenar los hospedadores por grupos de peso y estudiar las prevalencias, intensidades y abundancias medias de cada parásito, no se ha encontrado un patrón de comportamiento constante de los diferentes parásitos a lo largo de los grupos de peso. También se estudia qué ocurre con el parasitismo según la talla de los hospedadores, pues es este factor el que muestra la edad del animal. No se observaron diferencias de peso significativas en los hospedadores atribuibles a la carga de parásitos soportada. Por último se examinan cómo se asocian los diferentes parásitos en combinaciones multiparásitas.A preliminary study of the gill parasites from 91 common dentex (Dentex dentex, Pisces, Sparidae) was developed. Sample was formed by 61 wild fishes caught in waters of Mallorca and Menorca channel (Balearic Islands) and 30 farmed fishes from a cage located in the harbour of Mallorca. Eight parasite species were found: one dinoflagellate (Amyllodinium ocellatum), one monogenean (Microcotyle erythrini), one udonellidean (Udonella caligorum), one digenean trematode (Stephanostomum sp. metacercariae), three copepods (Caligus productus, Caligus diaphanus and Clavellotis fallax) and one isopod (Gnathia vorax, praniza larvae). The udonellidean U. caligorum was found as a hyperparasite or phoront of the three copepods. Prevalence, mean intensity and abundance and other ecological parameters as well as the spatial site of each parasite in the gill tissue are described. It also discusses the hypothetical damage that infections might cause in sea cage-farmed common dentex from the same area through interaction between wild and farmed common dentex populations. Positive correlations among the different parasites and the host conditions (size/weight) have not been found, so we could not affirm that the number of parasites increases with host body size. We only found positive correlations between both caligid copepods and between C. diaphanus and C. fallax. After grouping hosts in weight classes and studying the prevalence, mean intensity and abundance of each parasite, any of them showed a constant behavior pattern along such weight classes. Host size and parasitism is analyzed in order to know the possible relationship between parasitism and host age. No significative differences on host weight in relation with the parasitic burden were detected. The multiparasitic combinations are also examined.
7
Oosthuizen, Carel Jakobus. "Genetic variation within Cape stumpnose, Rhabdosargus holubi Steindachner (Teleostei: Sparidae)." Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-07092008-135620.
8
Day, Julia Jane. "Comparative morphology and evolutionary relationships of the Sparidae (Teleostei: Percoidei)." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326234.
9
Oosthuizen, Carel Jakobus. "Genetic variation within Cape stumpnose, Rhabdosargus holubi Steindachner (Teleostei: Sparidae)." Diss., University of Pretoria, 2006. http://hdl.handle.net/2263/26156.
Abstract:
Due to the nature of the marine environment genetic studies allow insight into behaviour and natural history that is difficult or impossible to identify by direct field observation. Current as well as historical population demography and gene flow can be detected by using molecular techniques. Genetic studies on only a few commercially important marine species along the South African coast have been conducted, although many marine fish species utilize estuaries as nursery areas and little attention has been afforded to studying larval distribution and recruitment of these species from a molecular point of view. Many of these estuarine associated species, especially in the South African milieu, are important for recreational and subsistence use. Associated with southern African estuaries are 13 species of the family Sparidae of which Cape stumpnose Rhabdosargus holubi is the most abundant. Juveniles are mostly confined to estuaries while the adults are strictly marine. Rhabdosargus holubi are serial spawners but temporally separated spawning peaks have been recorded along the South African coastline. Within the first part of this dissertation, the general characteristics of marine fish populations and the marine environment along the South African coast are being discussed. The main aim of this study was to determine the population genetic structure from estimates of nuclear and mitochondrial genetic variation across the distributional range of Rhabdosargus holubi. Samples were collected from 13 geographic localities along the South African coastline from St Lucia in the northeast to Klein River in the southwest. Juveniles were sampled in estuaries and adults were collected in the marine intertidal zone. Mitochondrial DNA control region fragments of 368 bp in length were obtained from a total of 214 individuals from all sampling localities. A total of 36 alleles were identified from 34 polymorphic sites. Following an allele homogeneity test, samples from different localities were lumped to represent six distinct geographical regions. Mitochondrial DNA control region analyses of juveniles showed high haplotype diversity and low nucleotide diversity with no divergent maternal lineages. No pattern between haplotype genealogy and geographic locality was evident. Population genetic analyses using heterologous microsatellite amplification have been successfully completed for a number of studies, including numerous studies of variation within marine fish species. Microsatellite studies have proven to be more sensitive in detecting subtle population structure than mtDNA and/or protein polymorphisms in high gene flow species. A total of 113 microsatellite loci previously isolated from phylogenetically closely related marine fish species were tested for amplification. The success rate of heterologous microsatellite amplification was extremely low (0.02%), with only two polymorphic loci amplifying consistently for analysing 133 individuals sampled from six localities along the distributional range of R. holubi. Results from these two loci were insufficient to draw conclusions about the population genetic structure of R. holubi along the South African coast. Possible reasons for the low rate of amplification success and future research recommendations are discussed. The findings from this study suggest that R. holubi is not geographically restricted, has high gene flow among localities and likely exist as a single stock.Dissertation (MSc (Genetics))--University of Pretoria, 2006.
Genetics
unrestricted
10
Isemonger, Devin Neil. "Modelling the spatial and genetic response of the endemic sparid: Polysteganus praeorbitalis (Pisces: Sparidae) to climate change in the Agulhas Current system." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/54509.
Abstract:
The Scotsman Seabream, Polysteganus praeorbitalis, is one of several large, slow-growing members of the Sparidae family of fishes endemic to the Agulhas Current system in the Western Indian Ocean (WIO). Relatively little research has been conducted on this species despite its importance to both recreational and commercial line fisheries in South Africa and the drastic decline in catch per unit effort (CPUE) that has been recorded since the 1940s. Changing sea temperatures as a result of global climate change are further expected to affect the distribution and abundance of many fish species based on their thermal tolerances, life histories and population structures. The ability of these species to shift their distribution and adapt to new environments and thermal conditions will depend to some degree on the levels of genetic variation and gene flow, within and between populations. A combined approach using species distribution modelling and genetic analyses may prove to be a useful tool in investigating the potential effects of climate change on the distribution and genetic diversity of species. An ensemble species distribution model (SDM) based on 205 occurrence records and 30 years of Reynolds Optimum Interpolated (OI) sea surface temperature data was constructed to predict the distributional response of P. praeorbitalis to climate change in the Agulhas Current system. The ensemble SDM displayed a true skill statistic (TSS) of 0.975 and an area under the receiver operating curve (ROC) of 0.999, indicating good model fit. Autumn and winter minimum temperatures, as well as bathymetry, were the most important predictor variables in the majority of models, indicating that these variables may directly constrain the distribution of P. praeorbitalis. In particular, the southern range edge of this species appeared to be constrained by autumn and winter minima, with high model agreement on this range edge. Conversely, the northern range limit showed poor model agreement leading to a gradual reduction in occurrence. This indicates that this range edge may be constrained by other factors not included in the models such as species interactions. The ensemble SDM projected the current range of P. praeorbitalis to be 1500 km², smaller than the published range for this species. The model underestimated the northern range edge of this species by approximately 5° latitude when binary transformed. This is probably due to the rarity of this species in the landings of the Mozambican linefishery, which was assumed to be an indication of low abundance of P. praeorbitalis in these waters. The absence of a specimen to verify the published northern range edge of this species indicates that the northern range edge produced by this model is likely to be closer to the actual range limit of the species. A range contraction of 30% occurring at both the northern and southern edge of P. praeorbitalis’ range and range fragmentation occurring, towards its northern range edge by 2030, was predicted. These changes are modelled to be the results of cooling related to the intensification of the Port Alfred upwelling cell and of warming predicted north of the Natal Bight and in southern Mozambique. Genetic analyses of the nuclear DNA (nDNA) S7 intron 1 and mitochondrial DNA (mtDNA) control region genes were carried out using 118 tissue samples of P. praeorbitalis collected at four main localities: the Eastern Cape, Transkei, southern KwaZulu-Natal and northern KwaZulu-Natal. Analyses of genetic diversity levels revealed relatively low diversity in the mtDNA dataset (Hd = 0.488; π = 0.004) and moderate levels of diversity in the nDNA dataset (Ad = 0.922; π = 0.005). The low levels of diversity observed in the mtDNA dataset might be explained by a number of factors, including high variation in spawning success, the negative effects of over-harvesting, or a recent population bottleneck. The last explanation is supported by characteristic star-shaped haplotype networks and unimodal mismatch distributions displayed by both datasets. These results, in conjunction with a significant (p = 0.005) negative Tajimas D value (-2.029) in the mtDNA dataset and significant (p = 0.0005) negative Fu’s F statistic in both the nDNA (F = -26.5) and mtDNA (F = -11.9) datasets, provide strong evidence for a recent population expansion after a bottleneck event in this species. Spatially, mtDNA diversity was highest in the Eastern Cape and lowest in the middle localities, while nDNA diversity showed the opposite pattern. These results may be indicative of differences in the sex ratio between localities, possibly as a result of the protogynous hermaphroditism that has been postulated for this species. Although pairwise comparisons and exact tests of population differentiation revealed no significant geneticdifferentiation between populations in the mtDNA dataset, there was some evidence of low levels of differentiation in the nDNA dataset. This occurred for comparisons between the Eastern Cape and Transkei (Fst = 0.039; p <0.05), and the northern KwaZulu-Natal (Fst = 0.045; p < 0.05).. This might be the result of one or a combination of factors including the effects of the Port Alfred upwelling cell on dispersal and gene flow, or the possibility of more than one spawning ground for this species promoting sub-structuring. A SAMOVA analyses run on the nDNA dataset maximised variance by grouping the Eastern Cape and southern KwaZulu-Natal together and Transkei and northern KwaZulu-Natal together in two groups. This revealed no evidence of spatial structure (p = 0.36), with only 3.30% of variation explained by this grouping. The removal of individuals below the estimated length at 50% maturity in the nDNA dataset, in order to test for temporal structure, resulted in stronger evidence of differentiation between the Eastern Cape and all other localities: Transkei (Fst = 0.081; p< 0.05), southern KwaZulu-Natal (Fst = 0.031; p<0.05), and northern KwaZulu-Natal (Fst = 0.078; p< 0.05). This indicates that some temporal genetic structure may exist between age classes within this species. The differentiation observed between the Eastern Cape and other localities, coupled with the high percentage of private haplotypes in the mtDNA dataset in this locality, indicates that this area is where P. praeorbitalis is most vulnerable to the potential negative effects of climate change on its genetic diversity. However, the vast majority of this species genetic diversity appears to reside towards the centre of its range where it is most abundant and the lack of strong genetic structure indicates high levels of gene flow. In conclusion, while P. praeorbitalis is vulnerable to range loss as a result of climate change, its genetic diversity is unlikely to be greatly affected.
11
Lang, Judy Brenda. "The growth characteristics of sparid otoliths." Thesis, Rhodes University, 1992. http://hdl.handle.net/10962/d1005129.
Abstract:
The periodicity of formation of growth increments in the otoliths of South African sparids was validated by the oxytetracycline labelling technique. Intramuscular injections of oxytetracycline at a dosage of 250mg/kg marked the otoliths of laboratory held juvenile sparids, while a dosage range of 50 - 100mg/kg oxytetracycline, injected intramuscularly, marked adult sparids in the field. Laboratory held, larval sparid otoliths were marked by immersion for 24hrs a solution of 100-150mg/l alizarin complexone. Both daily (microstructural) and annual (macrostructural) growth increments were identified in the otoliths. The micro incremental pattern of deposition in the sparid otoliths conformed to the general pattern of otolith structure. Sparid otoliths consisted of a central opaque nucleus composed of multiple primordia. surrounding this nucleus were daily increments which decreased in width as the distance from the nucleus increased. Both check rings and subdaily increments were visible throughout the otolith. Minor environmental changes did not affect micro incremental deposition. Narrow opaque and wide hyaline annual growth zones were identified in sectioned sparid otoliths. Scanning electron microscope analysis of the annual growth zones revealed that microincrements within the opaque zone were narrowly spaced with prominent discontinuous phases. This resulted in the greater optical density and higher protein content of the zone. The hyaline zone was composed of widely spaced daily increments with prominent incremental phases accounting for the translucent nature of this zone. Opaque zone formation in the otoliths of many South African sparids was found to occur primarily during periods of reproductive activity and was shown to be indicative of slow otolith growth. The hyaline zone was formed after the spawning season, representative of fast otolith growth. The results of this study have resolved much of the controversy surrounding the rate of growth and time of formation of the opaque and hyaline growth zones in South African sparid otoliths.
12
Faure, Beaulieu Nina. "Dedicated dads: a study on the nesting behaviour of Spondyliosoma emarginatum (Telostei: Sparidae)." Master's thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/33661.
Abstract:
Fish display the most diverse parental care behaviours within the animal kingdom. These behaviours are important from evolutionary and conservation perspectives as parental care is critical for the development and survival of the young. This study used video monitoring to uncover the nesting behaviour of an endemic southern African species of the Sparidae family, Spondyliosoma emarginatum (steentjie). S. emarginatum has evolved a nesting strategy by which males create nests on the seafloor for females to lay their eggs in. The eggs are fertilised and guarded by the male until they hatch. This species is particularly interesting as it has evolved a life-history strategy unique to the Sparidae, a combination of protogyny (female to male sex change) and male parental care. A compound nesting site with over 50 nests was discovered in 9 to 14 m depth in False Bay, South Africa. A large diversity in nest size and habitat was uncovered. The first nest with eggs appeared on the 3rd of September and this number gradually increased to a maximum of 26 nests on the 3rd of October. Eggs took from seven to nine days to hatch. During nesting, males were affected by stochastic weather events in the form of south-easterly gales. Nesting sites are likely limited to sheltered bays along South Africa's mostly exposed coast, and the optimal depth is probably a tradeoff between storm exposure and temperature. Deeper nests are expected in the east where the water is warmer. Nests were filmed daily to reveal how male behaviour changes before egg deposition and during egg development. After egg deposition, males increased their time on the nest from 30 to 52 minutes per hour. Nest defence included the regular clearing of invertebrate invaders (brittle stars, hermit crabs, sea cucumbers, and sea stars), and chasing away other fish species (sand gobies, Roman, and hottentot) and neighbouring male steentjies. Energy intensive behaviours such as clearing the nest and fanning the eggs remained constant irrespective of egg presence. In addition, males do not feed when guarding eggs, which explains the drop in male condition during spring. The revelation of this nesting site is useful for conservation and fishery management as the nests and nesting males are vulnerable to both fishing and seabed disturbances. Spondyliosoma spp. fulfil the requirements of the size-advantage model of protogyny. Their short life-span, in particular, their even shorter egg-laying life-span, classifies this species as an opportunist. This strategy may explain its success and numerical dominance in a wide range of biogeographic zones. The nesting behaviours shares much in common with freshwater opportunistic fish species and set it apart from the bulk of the Sparidae.
13
Hesp, Sybrand Alexander. "Biology of two species of sparid on the west coast of Australia." Hesp, Sybrand Alexander (2003) Biology of two species of sparid on the west coast of Australia. PhD thesis, Murdoch University, 2003. http://researchrepository.murdoch.edu.au/76/.
Abstract:
Various aspects of the biology of the tarwhine Rhabdosargus sarba and western yellowfin bream Acanthopagrus latus were studied. The studies on R. sarba have focused on populations in temperate coastal marine waters at ca 32 degrees S and the lower reaches of an estuary (Swan River Estuary) located at the same latitude and in a subtropical embayment (Shark Bay) at ca 26 degrees S, while those on A. latus were conducted on the population in the latter embayment.
A combination of a macroscopic and histological examination of the gonads demonstrated that R. sarba is typically a rudimentary hermaphrodite in Western Australian waters, i.e. the juveniles develop into either a male or female in which the ovarian and testicular zones of the gonads, respectively, are macroscopically undetectable. This contrasts with the situation in the waters off Hong Kong and South Africa, in which R. sarba is reported to be a protandrous hermaphrodite. However, it is possible that a few of the fish that are above the size at first maturity and possess, during the spawning period, ovotestes with relatively substantial amounts of both mature testicular and immature ovarian tissue, could function as males early in adult life and then change to females. Although R. sarba spawns at some time between late winter and late spring in Western Australia, spawning peaks later in the Swan River Estuary than in coastal, marine waters at the same latitude and Shark Bay, in which salinities are always close to or above that of full strength sea water, i.e. 35 0/00. While the males and females attain sexual maturity at very similar lengths in the Swan River Estuary and Shark Bay, i.e. L50s all between 170 and 177 mm, they typically reach maturity at an earlier age in the former environment, i.e. 2 vs 3 years old. Thus, length and consequently growth rate influence the timing of maturity rather than age. During the spawning period, only 9 % of the fish caught between 180 and 260 mm in nearshore, shallow marine waters had become mature, whereas 91 % of those in this length range over reefs were mature, indicating that R. sarba tends to move offshore only when it has become physiologically ready to mature. The L50s at first maturity indicate that the current minimum legal length in Western Australia (230 mm) is appropriate for managing this species.
Oocyte diameter frequency distributions, stages in oocyte development, duration of oocyte hydration and time of formation of post-ovulatory follicles in mature ovaries of Rhabdosargus sarba in the lower Swan River Estuary (32 degrees 03'S, 115 degrees 44'E) were used, in conjunction with data on tidal cycles, to elucidate specific aspects of the reproductive biology of this sparid in an estuarine environment. The results demonstrated the following. (i) Rhabdosargus sarba has indeterminate fecundity sensu Hunter et al. (1985). (ii) Oocyte hydration commences at about dusk (18:30 h) and is completed by ca 01:30-04:30 h, at which time ovulation, as revealed by the presence of hydrated oocytes in the ovarian duct and appearance of newlyformed post-ovulatory follicles, commences. (iii) The prevalence of spawning was positively correlated with tidal strength and was greatest on days when the tide changed from flood to ebb at ca 06:00 h, i.e. approximately when spawning ceases. Spawning just prior to strong ebb tides would lead to the transport of eggs out of the estuary and thus into salinities that remain at ca 35 0/00. The likelihood of eggs being transported downstream is further enhanced by R. sarba spawning in deeper waters in the estuary, where the flow is greatest. (iv) Although mature ovaries were found in R. sarba in the estuary between early July and December, the prevalence of atretic oocytes was high until September, when salinities started rising markedly from their winter minima. Batch fecundities ranged from 2,416 for a 188 mm fish to 53,707 for a 266 mm fish. The average daily prevalence of spawning amongst mature females during the spawning period of R. sarba caught in the lower estuary, i.e. July to end of October, was 36.5 %. Thus, individual female R. sarba spawned, on average, at intervals of ca 2.7 days in each spawning season. Female R. sarba with total lengths of 200, 250 and 300 mm were estimated to have a batch fecundity of 7,400, 20,100 and 54,800 eggs, respectively and annual fecundities of 332,000, 903,000 and 2,461,000 eggs, respectively.
Rhabdosargus sarba is shown to undergo size-related movements in each of the three very different environments in which it was studied. In temperate coastal waters, R. sarba settles in unvegetated nearshore areas and then moves progressively firstly to nearby seagrass beds and then to exposed unvegetated nearshore areas and finally to areas around reefs where spawning occurs. Although R. sarba spawns in the lower Swan River Estuary, relatively few of its early 0+ recruits remain in the estuary and substantial numbers of this species do not start reappearing in the estuary until they are ca 140 mm. In Shark Bay, R. sarba uses nearshore mangroves as a nursery area and later moves into areas around reefs. The maximum ages recorded for R. sarba in coastal marine waters (11 years) and Shark Bay (13 years) were far greater than in the lower Swan River Estuary (6 years). However, the maximum lengths recorded in these three environments were all ca 350 mm. Due to the production by size-related movements of differences amongst the lengths of R. sarba at given ages in different habitats in coastal marine waters, the composite suite of lengths at age was not fully representative of the population of this species as a whole in this environment. A von Bertalanffy growth curve, which was adjusted to take into account size related changes in habitat type, significantly improved the fit to the lengths at age of individuals in the composite samples for the population beyond that provided by the unadjusted von Bertalanffy growth curve. This resulted in the maximum difference between the estimates of length at age from the two growth curves, relative to the L derived from the unadjusted von Bertalanffy curve, reaching a value equivalent to 8 %. However, the maximum differences for the corresponding curves for populations in the lower Swan River Estuary and Shark Bay were far less, i.e. 1.7 and 3.2 %, respectively, and thus not considered biologically significant. Rhabdosargus sarba grew slightly faster in the lower Swan River Estuary than in either coastal marine waters or Shark Bay, possibly reflecting the greater productivity of estuarine environments.
Acanthopagrus latus is a protandrous hermaphrodite. Detailed macroscopic and histological examination of the gonads of a wide size range of fish, together with a quantification of how the prevalences of the different categories of gonad change with size and age and during the year, were used to elucidate the sequence of changes that occur in the ovotestes of A. latus during life. The scheme proposed in the present study for the protandrous changes in A. latus differed from those proposed for this species elsewhere, but was similar to that of Pollock (1985) for the congeneric Acanthopagrus australis. The ovotestes of functional males develop from gonads which, as in older juveniles, contain substantial amounts of testicular and ovarian tissue. Such ovotestes, and particularly their testicular component, regress markedly after spawning and then, during the next spawning season, either again become ovotestes in which the testicular zone predominates and contains spermatids and spermatozoa (functional males), or become ovotestes in which the ovarian zone predominates and contains vitellogenic oocytes (functional females). Once a fish has become a functional female, it remains a female throughout the rest of its life. The trends exhibited during the year by reproductive variables demonstrate that A. latus in Shark Bay typically spawns on a very limited number of occasions during a short period in August and September and has determinate fecundity. The potential annual fecundities of 24 A. latus ranged from 764,000 in a 600 g fish to 7,910,000 in a 2,050 g fish and produced a mean [plus-minus]1SE of 1,935,000 [plus-minus] 281,000. The total length at which 50 % of A. latus become identifiable as males (245 mm) is very similar to the current minimum legal length (MLL) of 250 mm, which corresponds to an age of 2.5 years less than the age at which 50 % of males become females. Current spawning potential ratios calculated over a range of alternative values for natural mortality (M) for A. latus in Shark Bay suggests that the present fishing pressure is sustainable, but that the current MLL should be reviewed if recreational fishing pressure continues to increase.
The age composition and von Bertalanffy growth parameters for Acanthopagrus latus have been determined. The relevant parameters were inserted into the empirical equations of Pauly (1980) and Ralston (1987) for estimating natural mortality (M). Total mortality (Z) was calculated using Hoenig's (1983) equations, relative abundance analysis and a simulation based on maximum age and sample size.The two point estimates for M for A. latus, which were both 0.70 year-1, greatly exceeded all estimates for Z (range 0.18 to 0.30 year-1), which is clearly an erroneous result. To resolve this problem of inconsistent estimates, a Bayesian approach was developed, which, through combining the likelihood distributions of the various mortality estimates, produced integrated estimates for M and Z that are more consistent and precise than those produced for these two variables using the above methods individually. This approach now yielded lower values for M than Z and a measure of fishing mortality that appears to be consistent with the current status of the fishery. This approach is equally applicable to other fish species.
14
Lamrini, Abdeljaouad. "Les Sparidae de la côte atlantique marocaine reproduction, croissance et exploitation de cinq espèces /." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37614920n.
15
Ensair, Hend Assiad M. "The biology of Boopsoidea inornata (Castelnau, 1861) and life history comparisons within the Sparidae." Doctoral thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/31412.
Abstract:
South African marine ichthyofauna has remarkable diversity across a range of biogeographic zones from cold-temperate to subtropical. Two families stand out here, both with high diversity and high rates of endemism to the region, namely Sparidae and Clinidae. The Sparidae are of greater interest because of their commercial importance, and conversely, their conservation status. Several are listed as threatened by the IUCN. The Sparidae is also the family with the greatest plasticity in life history characteristics of any vertebrate family, as they include gonochorism, rudimentary hermaphrodites, and both kinds of sequential hermaphrodites. Life history characteristics are known determinants of the resilience of fish species to fishing, and more generally of their response, either positive or negative, to any form of disturbance. Life history characteristics of most of the species of Sparidae, in South Africa and worldwide, have been studied, particularly those of commercial and conservation importance. Omissions include those that are small, with little commercial importance. This is an oversight, as there is much to be learned about life history strategies by studying the full spectrum of variation in the family, and particularly those variants which produce numerically, and therefore ecologically, significant population sizes. In this thesis, I study the life history and parasite community of one of South Africa’s most abundant seabreams in separate chapters. In the last chapter I take a fresh perspective on life history variation among fishes, by comparing four sympatric seabreams to describe the several dimensions along which life history trade-offs can occur without the confounding influences of environment and phylogeny. Boopsoidea inornata (Castelnau, 1861) is endemic to South Africa. Eight hundred and seventeen fishes were sampled from four locations: False Bay, Struisbaai, Goukamma and Port Elizabeth from 2012 to 2014. They ranged in size from 130 to 310 mm fork length. The diet of B. inornata was investigated in False Bay and Struisbaai using Prey-Specific Index of Relative Importance (%PSIRI). B. inornata is an omnivore, with a preference towards small sand- and reef-dwelling prey and has only limited intake of algae and small fish. Age and growth were assessed using sectioned otoliths. A clear seasonal pattern of band formations deduced from the frequency of opaque margins show that B. inornata lay down one opaque and one transparent band per year. B. inornata is a small species (L∞= 222.7 mm) with high longevity (tmax= 37). It is a rudimentary hermaphrodite. The ovaries hold up to 8000 vitellogenic eggs, which equates to an average 19 eggs per gram of body mass. This value is low compared with other seabream species. B. inornata females spawn repeatedly during the year, although there is more spawning activity in spring, than in other months. The sex ratio is heavily skewed towards females (1:3.35). The presence of post-ovulatory follicles together with hydrated oocytes indicates that the species is an indeterminate batch spawner. Length at 50% maturity was calculated based on gonads collected throughout the spawning season. Females mature at 178 mm FL, compared to 185 mm FL for males. Female GSI greatly exceeds male GSI, and, together with the sex ratio, suggests a polygamous mating system. One hundred and fifty B. inornata were collected from False Bay, Struisbaai, Goukamma and Port Elizabeth to investigate associated parasite assemblages. Eighty six percent of the sample was infected by parasites. Parasites infecting B. inornata have never before been recorded. Nineteen parasite taxa were found infecting B. inornata across all localities and included myxozoan, monogenean, digenean, cestode, nematode, copepod and isopod representatives. Three species of digenean metacercaria showed high prevalence of infection in B. inornata across all four localities. These included a Stephanostomum sp. infecting the gill arches of 61%, and two unidentified digeneans. The unidentified digenean metacercariae- 2 was found in the kidneys and musculature of 59% of the total sample and the unidentified digenean metacercariae-1 was found infecting the hearts of 47% of the total sample. Overall parasite assemblages were significantly different amongst all localities, with no significant difference in parasite assemblages among size classes, age classes or sex within localities. Fish life history is affected by environmental and biological factors but is also constrained by phylogenetic influences on morphology and physiology. In an attempt to expose the nature and extent of life history trade-offs, I compared four closely related and sympatric seabreams, namely Spondyliosoma emarginatum, Pachymetopon blochii, Rhabdosargus globiceps and Boopsoidea inornata. I contend that only by eliminating or reducing as far as possible the effect of environment, habitat and phylogeny can we expose real trade-offs. Samples of each species were obtained in every season from the south-western Cape, South Africa, to obtain measures of total length, mass, gonadosomatic index and condition. S. emarginatum is a nest-guarding, short-lived, protogynous hermaphrodite. P. blochii is a resident, group-spawner, engaging in sperm competition. R. globiceps is a moderately long-lived migrant with a sex ratio of 1:1, that also engages in sperm competition over a short spawning season. B. inornata is a polygamous, long-lived resident with low annual fecundity, but a protracted spawning season. Although all four species are periodic strategists, life history trade-offs exist between several sets of variables, namely semelparity vs iteroparity, age-at-maturity vs maximum size, annual fecundity vs longevity, length of spawning season vs parental care, and length of spawning season vs migration. The efficiency of the sequential hermaphrodite strategy which allows every fish to spawn as a female until they are large enough to act as a male makes one question the rarity of this strategy. I argue that halving of the female life-span compromises the periodic strategy, and that hermaphroditism is at odds with migration. The latter rests on the assumption that the migrant social structure is based on cooperation, for feeding, defence and navigating in schools, whereas the hermaphrodite social structure is based on aggression and dominance hierarchies which requires residency and territoriality. No clear adaptive reason for the divergence among the sympatric species can be identified, although competition among the young is a candidate. This comparison reveals a wide range of options available to seabreams and shows how disparate life histories can be equally adaptive under identical conditions. More generally I have shown how a variety of life-history traits, such as migration, sex-ratio, reproductive strategy and somatic growth form interact to define a life-history.
16
Grant, Gareth Neil. "Movement patterns of Cape stumpnose, Rhabdosargus holubi (Sparidae), in the Kowie Estuary, South Africa." Thesis, Rhodes University, 2016. http://hdl.handle.net/10962/982.
Abstract:
Rhabdosargus holubi is an ubiquitous estuary-dependent fishery species endemic to southern Africa. Although aspects of its recruitment dynamics from sea to estuary have received considerable research attention, little is known about its movement behaviour within estuarine systems. Fishery surveys have also revealed that R. holubi is a dominant species in catches within several temperate estuaries in South Africa. Therefore, investigating movement behaviour is fundamental to understanding the ecology of this species and providing a means for implementing effective fisheries management strategies. This study made use of passive acoustic telemetry to quantify the movement patterns of juvenile R. holubi in the Kowie Estuary, in the Eastern Cape Province of South Africa. Previous studies have revealed that surgically implanted transmitters may have adverse effects on the physiology and behaviour of tagged fish. Therefore, due to the small size of juvenile R. holubi, an a priori transmitter-effect experiment was undertaken. This experiment revealed that juvenile R. holubi (146-217 mm fork length) were not adversely affected by the surgical implantation of acoustic transmitters (7 mm Ø, 1.6 g out of water) and hence acoustic telemetry was well suited to monitoring the movements of this species. A 4-month telemetry study evaluated the movement patterns of 21 juveniles (140-190 mm fork length) tagged in three equal batches along the length of the estuary. Specific aspects of their movement included space use patterns, habitat connectivity, and the influences of geophysical cycles and environmental variables. Tagged fish exhibited high residency, which varied between each release site area. The mean length of estuary used was greater for the upper batch (15.65 ± 6.49 km) than the middle and lower batches (7.36 ± 3.68 and 2.67 ± 2 km, respectively). In terms of habitat connectivity, once the tagged fish left the estuary, they generally did not return. Tagged R. holubi spent the majority (83%) of their monitoring periods within the estuarine environment, with the sea (16%) and riverine (1%) environments being utilised to a lesser extent. Diel and tidal cycles influenced the movement patterns of juvenile R. holubi. However, the high levels of residency meant that fine-scale movements were difficult to detect due to the acoustic receiver deployment configuration (i.e. receivers moored one kilometer apart). The influence of environmental variables on the movement of individuals, modelled with general linear mixed models (GLMMs), revealed that the effects of river inflow and water temperature were greatest. Increased river inflow caused individuals to use larger portions of the estuary. Increased water temperature, particularly river temperature, caused individuals to shift their distributions downstream (towards the mouth of the estuary). This study highlighted the importance of estuarine nursery habitats to R. holubi, suggesting that a loss or reduction of healthy estuarine habitats may lead to significant declines in the abundance of this species. Furthermore, extreme resident behaviour suggests that no-take area closures (estuarine protected areas) would be an effective management strategy for this important fishery species.
17
Henriques, Paulo Jorge Chaves dos Santos. "Estudo da eco-etologia de diplodus vulgaris (pisces: sparidae)- padrões agonísticos e estruturação social." Master's thesis, Instituto Superior de Psicologia Aplicada, 1997. http://hdl.handle.net/10400.12/585.
Abstract:
Dissertação de mestrado em EtologiaOs principais desideratos deste trabalho baseiam-se no estabelecimento do reportório comportamental básico e organização social de Diplodus vulgaris, como forma de resposta às pressões ambientais, que podem favorecer ou inibir, em maior ou menor grau, as várias modalidades do comportamento agonístico. O sistema agonístico de D. vulgaris é constituído por padrões comportamentais que envolvem sinais de intimidação, fuga e submissão. Alguns destes elementos implicam confrontação física directa, enquanto outros envolvem manobras no sentido de uma aparente redução do potencial atacante dos oponentes. Salienta-se a grande plasticidade alimentar da espécie - diversos padrões alimentares e alimentação em cardume - como forma de adaptação às condições adversas do meio, no sentido de uma máxima rentabilização energética ( associada à busca e procura de alimentos ), com a redução dos riscos de predação. Realizaram-se observações na natureza e em condições controladas, de juvenis em cativeiro, de modo a registar o efeito dos factores densidade e tamanho relativo dos indivíduos, na frequência e duração dos comportamentos agonísticos. Os resultados evidenciam que uma diminuição da densidade, conduz a um aumento da frequência dos comportamentos agonísticos ( embora apenas o padrão de mostra de dorsal apresente diferenças significativas ), e das durações de investidas, perseguições e fugas. A permanência de um indivíduo de tamanho relativo superior, aos restantes elementos do grupo, conduz a um aumento significativo das investidas, perseguições, fugas e cargas, bem como uma maior duração de mostra de dorsal, investida, perseguição e fuga. A análise de sequências de comportamentos agonísticos traduz uma certa padronização nas suas interacções agonísticas, realçando o papel fulcral na avaliação entre os indivíduos, desempenhado pelo padrão comportamental de mostra de dorsal ( que funciona como sinal ofensivo, mas não imediatamente agressivo ). Quando se registam assimetrias de tamanho entre os peixes, verifica-se que os de maior porte tendem a evoluir para padrões agonísticos associados a uma superioridade crescente: investida —> perseguição —> carga ou mordida, enquanto que os indivíduos de menores dimensões executam comportamentos de fuga e de submissão. A vivência em grupo indicia-se como o padrão geral de estruturação social da espécie, assente sobretudo na defesa de uma área ( abrigo ), associada a zona de protecção, repouso e reprodução, no interior da qual se observa uma diferente ocupação do espaço por parte dos indivíduos, expressa em termos agonísticos. Destacam-se as estruturas biológicas envolvidas na coordenação dos actos agressivos, garantes da adaptação da espécie ao meio, mediante o desenvolvimento de mecanismos que permitem minimizar os confrontos físicos directos e/ou os danos subsequentes.
18
au, corey wakefield@fish wa gov, and Corey Brion Wakefield. "Latitudinal and temporal comparisons of the reproductive biology and growth of snapper, Pagrus auratus (Sparidae), in Western Australia." Murdoch University, 2006. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20080530.105016.
Abstract:
This study focused on obtaining sound quantitative data on the reproductive biology, length and age compositions and growth of the snapper Pagrus auratus in the waters off Carnarvon at ca 25oS and Perth at ca 32oS on the west coast of Australia and at ca 34oS on the south coast of Western Australia. Sampling thus encompassed both sub-tropical and temperate waters and the geographical range within which this species is abundant in Western Australia. The resultant data were used to explore the ways in which the biological characteristics of P. auratus differ with latitude and thus water temperature. An intensive sampling regime for eggs and spawning individuals of P. auratus was conducted in Cockburn Sound, a large marine embayment in the Perth region at ca 32oS. The resultant data were used to elucidate where and when spawning occurs in this large marine embayment and to determine more precisely the factors that influence the timing of spawning. The implications of the results presented in this thesis for the management of P. auratus, a species that has been subjected to very heavy fishing pressure in recent years, are discussed.
The time and duration of spawning of P. auratus in the subtropical waters of Carnarvon differed markedly from those recorded for this sparid in the temperate and cooler waters of the Perth and the south coast regions. Spawning at Carnarvon occurred predominantly in the five months between late autumn (May) and mid spring (September), whereas it took place mainly in the three months between mid spring (October) and early summer (December) in the Perth region. Spawning of P. auratus on the south coast occurred predominantly in October and November in 2003 and 2004 and scarcely at all in 2005. Gonadal recrudescence was thus initiated when water temperatures were close to their maximum but declining in Carnarvon, and close to their minima and rising in the Perth and south coast regions, respectively. The prevalence of fully mature and spawning females in all three regions was greatest in those months when water temperatures lay between 19 and 21oC. Collation of the data in this thesis and those provided in the literature for other populations showed that the spawning period was related to latitude, occurring far earlier in sub-tropical than temperate waters.
The females and males attained maturity at a far smaller total length (L50) in the Carnarvon region, i.e. 378 and 353 mm, respectively, than in the Perth region, 585 and 566 mm, respectively, and also the south coast region, i.e. 600 and 586 mm. The trends exhibited by the age at maturity parallel those for length, with the A50s for the two sexes increasing from ca 4 years in Carnarvon to ca 5.6 years in the Perth region and nearly 7 years in the south coast region. The L50 and A50 at maturity thus both increased with increasing latitude.
Marginal increment analysis demonstrated that, irrespective of the number of opaque zones in the otoliths of P. auratus, a single such opaque zone is laid down each year in these otoliths. Furthermore, the trends exhibited by the monthly marginal increments showed that the opaque zone is laid down predominantly in winter in the subtropical waters of Carnarvon, as opposed to mainly in spring in the temperate waters of the Perth and south coast regions. Thus, the timing of formation of the opaque zone in the otoliths of P. auratus along the Western Australian coast is not related to the trends exhibited by water temperature, but, in both the Carnvarvon and Perth regions, was coincident with the timing of spawning.
The maximum total lengths recorded for females and males in the Carnarvon region, i.e. 864 and 840 mm, respectively, were considerably less than the corresponding values of 1051 and 1056 mm in the Perth region, and 1083 and 1099 mm in the south coast region. Growth in the Perth and south coast regions was greater than in Carnarvon, as is reflected in, for example, the respective lengths of 820, 720 and 610 mm for females at 10 years of age, as determined from the von Bertalanffy growth equations.
The length and age compositions in the Carnarvon and south coast regions were essentially unimodal, whereas those in the Perth region were bimodal. However, the mode in the length-frequency distribution for the south coast region was located well to the right of that in the Carnarvon region, reflecting relatively lower contributions by individuals of the age cohorts of 3 to 6 years. The marked bimodality in the length-frequency distribution for P. auratus in the Perth region was due to the presence of a group of mainly smaller individuals caught outside Cockburn Sound and another of mainly larger individuals that were caught in Cockburn Sound and which formed part of a spawning aggregation in that embayment.
The proportion of fish > 10 years old in the Carnarvon region declined markedly between 2003 and the following two years, presumably reflecting the effect of heavy fishing pressure. This contributed to the decision by fisheries managers to reduced the TAC in those waters after 2003. Age-frequency data demonstrated that annual recruitment success in Cockburn Sound varied greatly, with the 1991, 1992 and 1996 year classes being particularly strong, and recognizing that the relative numbers of the first two year classes did decline progressively between 2002 and 2004. Annual recruitment was particularly variable in the south coast region, with the catches of the 1996 year class dominating the samples.
The relative number of early stage P. auratus eggs in ichthyoplankton samples collected from Cockburn sound on each of four new moons during the spawning seasons of four consecutive years peaked in November in three of those years, i.e. 2001, 2003 and 2004, and in November/December in the remaining year, i.e. 2002. This showed that spawning in this embayment peaked during these months, at which times the mean sea surface temperatures ranged only from 19 to 20oC.
The prevalence of spawning fraction females in sequential samples demonstrated that spawning peaks at the new and, to a lesser extent, full moons. This helps account for the strong positive correlation between spawning fraction and tidal regime, with spawning being greatest when the tidal range is greatest.
Spawning times, back-calculated from the ages of the eggs collected during ichthyoplankton surveys in Cockburn Sound on each of 16 new moons within the spawning periods of four successive years, demonstrated that, in this embayment, P. auratus spawns at night and within the first three hours of the onset of the ebb tide. The distribution of egg concentrations on the 16 new moons showed that, each year, spawning occurred firstly in the north-eastern area of Cockburn Sound and then in the middle and finally north-western areas of this embayment.
In the Perth region, the marine embayments of Cockburn and Warnbro Sound act as nursery areas for P. auratus during the first two years of life. The majority of 2 to 5 year old fish and a large proportion of the 6 year old fish occupy the marine waters outside the embayments. The remaining 6 year old and almost all of the older fish begin to move in September into particularly Cockburn Sound, where they form relatively large spawning aggregations between October and December, before undergoing a massive emigration from this embayment in December/January. The limited returns from fish that were tagged in Cockburn Sound and were subsequently caught outside this embayment indicate that, following spawning, P. auratus does not tend to move in a particular direction.
Pagrus auratus stocks are heavily exploited in offshore, oceanic waters and in embayments, such as Cockburn Sound, where they are particularly susceptible to capture because of the tendency of this species to form spawning aggregations in these same easily accessible locations each year. The data obtained during this thesis show that the L50 at maturity of females and males in temperate waters, i.e. nearly 600 mm, is far greater than the current minimum legal length (MLL) of 410 mm TL. There is thus a need to increase the MLL and/or reduce fishing pressure on immature individuals in open waters. However, the effectiveness of an increase in the MLL may be limited because there is evidence that P. auratus suffers from fishing-induced barotrauma. Closures of specific areas during the spawning season of P. auratus, such as those that have been applied in Cockburn Sound and Shark Bay, are potentially a very effective method for reducing the effects of heavy fishing on spawning individuals.
19
Lee, King-yiu. "Molecular cloning and characterization of gonadotropin-releasing hormone receptors in the black seabream (Mylio macrocephalus)." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22823876.
20
Brouwer, Stephen Leonard. "Biology, population dynamics and management of carpenter (Argyrozona argyrozona) an endemic South African reef fish." Thesis, Rhodes University, 2005. http://hdl.handle.net/10962/d1005084.
Abstract:
Carpenter, Argyrozona argyrozona (Valenciennes, 1830), is an endemic South African sparid fish. They form an important component of the commercial linefishery on the South African east coast, where they are the third most important species landed. Recent investigations revealed that the catch per unit effort (cpue) of this species has declined markedly since the early 1900’s. Despite these declines and the importance of this resource, remarkably little biological information on this species exists for providing management advice. This thesis investigates the life history of carpenter, particularly those aspects that are used for management. This includes an investigation into the stock distribution and identification of nursery areas, and an assessment of age, growth, reproduction and movement patterns. Age and growth was assessed using methods based on both otoliths and mark-recapture. Transverse sagittal sections from the Tsitsikamma National Park showed clear opaque and translucent growth increments. Marginal growth zone analysis and mark-recapture of chemically tagged fish (Oxytetracycline) revealed that these were deposited on an annual basis: opaque in summer and translucent in winter. A. argyrozona were found to be long lived (up to 27 years) and slow growing. Within reader (between counts) and between readers average percent error (APE) was 5.3 and 1.8, respectively, showing that readability of carpenter otoliths is high. Comparison between whole and sectioned otoliths showed that the former significantly under-estimated the age of fish older than 10 years (p<0.01). A large proportion (68%) of the individual growth rates derived from mark-recapture data were below those predicted by the otolith based von Bertalanffy growth model (p<0.01). This was attributed to the negative influence of external tags, as hydroids, frequently occurring on the tags of recaptured fish, were observed to cause severe lesions and in some cases, extensive fin damage. This brings into question the use of mark-recapture studies to calculate growth of some species. The effects of sampling design and sample size on age and growth estimation were assessed. The minimum sample size required to accurately estimate growth and mortality, and the effects of using either random or stratified sampling procedures were tested. Decimal and integer ageing both produced similar estimates of von Bertalanffy growth parameters, growth curves, spawner biomass-per-recruit (SB/R) and fishing mortality (F) estimates. Sampling monthly throughout the year and collecting data in a single large sample provided similar growth curves, von Bertalanffy, F and SB/R estimates. The data showed that estimates based on less than 300 random samples were unreliable. However, accurate growth parameter estimates were achievable with less than 200 samples if the sample was stratified with 10 or more samples per 2 cm size class. An investigation into the reproductive biology of A. argyrozona within the Tsitsikamma National Park revealed that they were serial spawning late gonochorists. The size at 50% maturity (L₅₀) was estimated at 292 and 297 mm FL for females and males, respectively. Both monthly gonadosomatic indices and macroscopically determined ovarian stages strongly suggest that A. argyrozona within the Tsitsikamma National Park spawn in the austral summer between November and April. The presence of post-ovulatory follicles (POF's) confirmed the six month spawning season, while monthly proportions of early (0-6 hour old) POF's showed that spawning frequency was highest (once every 1-2 days) from December to March. Although spawning season was more highly correlated to photoperiod (r = 0.859) than temperature (r = -0.161), the daily proportion of spawning fish was strongly correlated (r = 0.93) to ambient temperature over the range 9-22⁰C. Both spawning frequency and season increased with fish length. As a result of the allometric relationship between annual fecundity and fish mass a 3 kg fish was calculated to produce 5 fold more eggs per kilogram of body weight than a fish of 1 kg. In addition to producing more eggs per unit weight each year, larger fish also produce significantly larger eggs. Adult emigration and larval dispersal of A. argyrozona from the Tsitsikamma National Park (TNP), South Africa, were investigated using mark-recapture data and Acoustic Doppler Current Profiler measurements of currents. Tagging data showed that adult carpenter were mainly resident, with a small proportion (7%) leaving the TNP in both easterly and westerly directions. No relationship was found between fish movement patterns and fish size or time-at-liberty. Current patterns suggest that eggs and larvae spawned within the TNP are mainly transported eastwards towards established nursery grounds; the median estimated distance moved was 299 km (range 42-561 km) in 30 days (time to flexion). Given this pattern of ichthyoplankton dispersal together with the fact that adult carpenter within the TNP display a high degree of residency and that they are much more abundant than in adjacent fishing grounds (cpue = 23 times greater), it appears that the TNP protects a viable carpenter spawner population capable of seeding adjacent fishing grounds. Fishery independent biomass surveys and commercial linefish catch returns were used to elucidate the spatial patterns of A. argyrozona distributed along the South African continental shelf. Two distinct areas of abundance were determined, one on the central and the other on the eastern Agulhas Bank. Tagging studies revealed little exchange between them. Two distinct nursery areas were identified. These data suggest that in each area juvenile A. argyrozona settle and move inshore, and then move offshore as they grow. Otolith readability and growth rates varied between regions, with fish from the Eastern Cape having the lowest average percentage error and the slowest growth rates, readability decreased westward. L₅₀ varied between the central and eastern Agulhas Bank as did mass at length. Based on the distribution of carpenter, variability in otolith readability, mass at length, variation in growth and size at maturity, it is concluded that carpenter exist as two separate stocks, one on the central Agulhas Bank and the other on the eastern Agulhas Bank. SB/R, fecundity-per-recruit (Egg/R) and yield-per-recruit (Y/R) models were used to model both South African carpenter stocks. Owing to the allometric relationship between annual fecundity and individual size, Egg/R ratios were between 40 and 74% of SB/R at equivalent F. Egg/R ratios account for allometric increases in fecundity with size/age, and are therefore regarded as more accurate estimates of reproductive potential, and biological reference points for per-recruit analysis should wherever possible be based on this quantum. It is shown that the current length at first capture (lc) (250 mm TL) and F (at M = 0.1) will reduce Egg/R to 6.41% of the pristine value in the Eastern Cape and between 6.06 and 14.15% on the central Agulhas Bank, indicating that both stocks are heavily over exploited. An increase in lc from 250 to 350 mm TL and a 70% reduction in commercial fishing effort is recommended to attain a target reference point of 40% Egg/RF=0. Bag frequency analysis indicates that a reduction in daily bag limit from 10 to 4 fish.person¹.day⁻¹ would effect an equivalent reduction in recreational F. The trawl bycatch of carpenter is only 3% of the reported line catch, consequently restrictions to this fishery are not recommended.
21
Winkler, Alexander Claus. "Taxonomy and life history of the zebra seabream, Diplodus cervinus (Perciformes: Sparidae), in southern Angola." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1012062.
Abstract:
The zebra sea bream, Diplodus cervinus (Sparidae) is an inshore fish comprised of two boreal subspecies from the Gulf of Oman and the Mediterranean / north eastern Atlantic and one austral subspecies from South Africa and southern Angola. The assumption of a single austral subspecies has, however, been questioned due to mounting molecular and morphological evidence suggesting that the cool Benguela current is a vicariant barrier that has separated many synonymous inshore fish species between South Africa and southern Angola. The aims of this thesis are to conduct a comparative morphological analysis of Diplodus cervinus in southern Angola and South Africa in order to classify the southern Angolan population and then to conduct a life history assessment to assess the life history impact of allopatry on this species between the two regions. Results of the morphological findings of the present study (ANOSIM, p < 0.05, Rmeristic = 0.42) and (Rmorphometric = 0.30) along with a concurrent molecular study (FST = 0.4 – 0.6), identified significant divergence between specimens from South Africa (n = 25) and southern Angola (n = 37) and supported stock separation and possibly sub-speciation, depending on the classification criteria utilised. While samples from the two boreal subspecies were not available for the comparative morphological or molecular analysis, comparisons of the colouration patterns between the three subspecies, suggested similarity between the southern Angola and the northern Atlantic / Mediterranean populations. In contrast, the colouration patterns between the southern Angolan and South African specimens differed substantially, further supporting the morphological and molecular results. The distinct morphological divergence between the southern Angolan and South African populations was not reflected within the life history traits of both populations. A combination of methods, including length/age frequency analyses, adult sex ratios and histological analysis was used to determine that this species is a rudimentary hermaphrodite in southern Angola. Peak spawning season was observed between June and July. The overall sex ratio (M: F) was 1:1.52 with females dominating smaller younger size classes and 50% maturity was attained at 210 mm FL and 4.6 years. Females [L(t) = 287.5(1-e⁻°·¹⁸⁽t⁻²·⁸⁴⁾)] grew significantly faster (LRT, p < 0.05) than males [L(t) = 380.19(1-e⁻°·°⁶⁽t⁻⁷·¹²⁾)]. The higher maximum age of the southern Angolan population of D. cervinus (43 years) was older than that of South African individuals sampled in the tsitsikamma national park. The similarities in the life history of the two austral populations are probably a consequence of similar selective pressures in the similar warmtemperate habitats. Evidence to support the above comments was found in the feeding study which showed that the South African and Angolan populations were almost identical, with both populations feeding primarily on amphipods and polychaete worms throughout ontogeny. In contrast, the diet of their boreal conspecifics from the Mediterranean was different, where larger individuals tended to select larger, and more robust, prey items. The life history differences observed between the boreal and austral populations can be attributed to either sampling bias or environmental factors. Sampling biases included the use of different age and growth estimation techniques, while the environmental factors would include differential selective pressures most likely driven by different resource availability and exploitation. The present study provides crucial baseline life history information of a potentially exploitable species off southern Angola as well as information on the life history plasticity of the species. Unfortunately, the current lack of uniformity in the methods used to estimate life history parameters between studies conducted on the boreal and austral populations have complicated our understanding of the evolution of various life history trends in sparid fish. From a management perspective however, the results from the present study can be used to propose management strategies for an emerging trap fishery in southern Angola. Using a balanced exploitation fishery approach (harvesting up to the size-at-100% maturity), the size of the fish traps entrance was calculated based the morphological information from this and other small sparid species that are targeted and was estimated to be 62 mm.
22
Bennett, Rhett Hamilton. "Movement patterns, stock delineation and conservation of an overexploited fishery species, Lithognathus Lithognathus (Pisces: Sparidae)." Thesis, Rhodes University, 2012. http://hdl.handle.net/10962/d1015709.
Abstract:
White steenbras Lithognathus lithognathus (Pisces: Sparidae) has been a major target species of numerous fisheries in South Africa, since the late 19th century. Historically, it contributed substantially to annual catches in commercial net fisheries, and became dominant in recreational shore catches in the latter half of the 20th century. However, overexploitation in both sectors resulted in severe declines in abundance. The ultimate collapse of the stock by the end of the last century, and the failure of traditional management measures to protect the species indicate that a new management approach for this species is necessary. The species was identified as a priority for research, management and conservation in a National Linefish Status Report. Despite knowledge on aspects of its biology and life history, little is known about juvenile habitat use patterns, home range dynamics and movement behaviour in estuaries. Similarly, the movement and migration of larger juveniles and adults in the marine environment are poorly understood. Furthermore, there is a complete lack of information on its genetic stock structure. Such information is essential for effective management of a fishery species. This thesis aimed to address the gaps in the understanding of white steenbras movement patterns and genetic stock structure, and provide an assessment of its current conservation status. The study adopted a multidisciplinary approach, incorporating a range of methods and drawing on available information, including published literature, unpublished reports and data from long-term monitoring programmes. Acoustic telemetry, conducted in a range of estuaries, showed high site fidelity, restricted area use, small home ranges relative to the size of the estuary, and a high level of residency within estuaries at the early juvenile life stage. Behaviour within estuaries was dominated by station-keeping, superimposed by a strong diel behaviour, presumably based on feeding and/or predator avoidance, with individuals entering the shallow littoral zone at night to feed, and seeking refuge in the deeper channel areas during the daytime. Conventional dart tagging and recapture data from four ongoing, long-term coastal fish tagging projects, spread throughout the distribution of this species, indicated high levels of residency in the surf zone at the late juvenile and sub-adult life stages. Consequently, juvenile and sub-adult white steenbras are vulnerable to localised depletion, although they can be effectively protected by suitably positioned estuarine protected areas (EPAs) and marine protected areas (MPAs), respectively. It has been hypothesized that adult white steenbras undertake large-scale coastal migrations between summer aggregation areas and winter spawning grounds. The scale of observed coastal movements was correlated with fish size (and age), with larger fish undertaking considerably longer-distance coastal movements than smaller individuals, supporting this hypothesis. Given the migratory behaviour of adults, and indications that limited spawning habitat exists, MPAs designed to protect white steenbras during the adult life stage should encompass all known spawning aggregation sites. The fishery is plagued by problems such as low compliance and low enforcement capacity, and alternative management measures, such as seasonal closure, need to be evaluated. Despite considerable conventional dart tagging effort around the coastline (5 782 fish tagged) with 292 recaptures there remains a lack of empirical evidence of fish migrating long distances (> 600 km) between aggregation and spawning areas. This uncertainty in the level of connectivity among coastal regions was addressed using mitochondrial DNA sequencing and genotyping of microsatellite repeat loci in the nuclear genome, which showed no evidence of major geographic barriers to gene flow in this species. Samples collected throughout the white steenbras core distribution showed high genetic diversity, low genetic differentiation and no evidence of isolation by distance or localised spawning. Although historically dominant in several fisheries, analysis of long-term commercial and recreational catch data for white steenbras indicated considerable declines and ultimately stock collapse. Improved catch-per-unit-effort in two large MPAs subsequent to closure confirmed that MPAs can be effective for the protection of white steenbras. However, the current MPA network encompasses a low proportion of sandy shoreline, for which white steenbras exhibits an affinity. Many MPAs do not prohibit recreational shore angling, which currently accounts for the greatest proportion of the total annual catch. Furthermore, EPAs within the juvenile distribution protect a negligible proportion of the total available surface area of estuaries – habitat on which white steenbras is wholly dependent. Despite some evidence of recent increases in abundance in estuaries and the surf zone in certain areas, white steenbras meets the criteria for “Endangered” on the IUCN Red List of Threatened Species, and for “Protected species” status on the National Environmental Management: Biodiversity Act of South Africa. The species requires improved management, with consideration for its life-history style, estuarine dependency, surf zone residency, predictable spawning migrations and its poor conservation status. The multidisciplinary approach provides valuable information towards an improved scientific basis for the management of white steenbras and a framework for research that can be adopted for other overexploited, estuarine-associated coastal fishery species.
23
Richardson, Timothy John. "The taxonomy, life-history and population dynamics of blacktail, Diplodus Capensis (Perciformes: Sparidae), in southern Angola." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005170.
Abstract:
The blacktail, Diplodus capensis, is an inshore sparid fish distributed from Mozambique to Angola. This species forms an important component of coastal fisheries within its distribution, one being the subsistence handline fishery in southern Angola. With this fishery being critically important to the livelihoods of local communities, a biological study and stock assessment was conducted to provide information for the management of this species in southern Angola. However, with molecular evidence suggesting that the Benguela current may have separated the southern African populations of many inshore fish species over two million years ago, a morphological, taxonomic analysis was considered necessary to first investigate whether there was evidence for allopatry in this species. A total of 46 morphometric measurements and 18 counts were carried out on specimens collected from various locations in southern Angola and South Africa. Results were analysed using multi-dimensional scaling (MDS) and the significance of clusters was tested using analysis of similarities (ANOSIM). Biological samples of D. capensis were collected monthly from an unexploited area from April 2008 to March 2009. Additional biological samples were collected from the subsistence fishers in an exploited area during May, June and December 2009. Standard biological laboratory techniques were employed for the lifehistory comparison between the exploited and unexploited area. A per-recruit analysis was conducted using the life-history parameters from both areas in order to assess the current status of the subsistence fishery and to investigate the potential short-falls of the per-recruit assessment approach. The morphometric comparison showed that there was not sufficient evidence for speciation between the southern Angolan and South African populations of D. capensis. There was, however, sufficient morphological evidence to suggest that these populations are separate stocks. This indicated that the existing reference points on which the management of the South African population is based are unsuitable for the Angolan population. Diplodus capensis in southern Angola is omnivorous, feeding predominantly on algae, barnacles and mussels. An ontogenetic shift from algae to barnacles and mussels was correlated with allometric growth patterns in their feeding apparatus. This species is a rudimentary hermaphrodite in southern Angola with peak spawning in June and July. The overall sex ratio (M: F) was 1: 4.7 in the unexploited area and 50% maturity was attained at 149.5mm FL and five years. Diplodus capensis in southern Angola exhibits very slow growth with the maximum age observed being 31 years (validated using mark recapture of chemically injected fish). Females [L(t) = 419.5(1-e⁻°·°⁴⁵⁽t⁻³·⁴ ⁾)] grew significantly faster (LRT, p < 0.05) than males [L(t) = 297.4(1-e⁻°·°⁷⁷⁽t⁻²·⁷⁾)], and females dominated the larger size classes and older age classes. In the exploited area, the length and age frequencies were severely truncated, the maximum observed age was greatly reduced (17 years) and the sex ratio was less female biased at 1: 2.2. Although there was no evidence for a physiological response to exploitation through alterations in growth or size/age at sexual maturity between the two areas, there was an increase in the proportion of small females in the exploited area, which may have been a compensatory response for the loss of large females. A combination of an underestimate of longevity, different estimates of the Von Bertalanffy growth parameters and overestimates of the natural mortality rate in the exploited population resulted in a 92% underestimate of the pristine spawner biomass-per-recruit (SBR) value. An assessment based on the actual pristine SBR estimate from the unexploited area revealed that the subsistence fishery had actually reduced D. capensis to 20% of its pristine SBR levels and highlighted the value of pre-exploitation life-history information for the application of per-recruit models. This study has shown that D. capensis in southern Angola displays life-history characteristics that render it susceptible to overexploitation, even at low levels of fishing pressure. The current lack of infrastructure and enforcement capacity in the fisheries department of Angola renders traditional linefish regulatory tools, such as size limits, bag limits and closed seasons, inappropriate. Therefore, suitably designed marine protected areas are recommended as the best management option for this species.
24
Bause, Mariëtte. "The challenge of applying systematic conservation planning to the marine environment using expert knowledge (focus: Sparidae)." Thesis, University of Port Elizabeth, 2004. http://hdl.handle.net/10948/343.
Abstract:
Although the marine environment has generally been considered to be less in need of attention from conservationists, politicians and managers than the terrestrial environment, there has been an increasing appreciation that there is little left in the marine environment that can be considered unaltered by humans. Conservation action is therefore urgently needed to protect marine populations, species and environments from anthropogenic pressures. Since overharvesting seems to be the main cause of the collapse in coastal ecosystems, areas need to be protected so that stocks can recover. However, the proclamation of such marine protected areas (MPAs) need to be well planned to ensure that species are well represented and that their biological requirements are met in the long term. While terrestrial conservation planners have started to incorporate biological, social and economic information into so-called systematic conservation plans, marine planners have been more hesitant to use these approaches due to the greater openness of the ocean (with the associated greater dispersal of marine organisms and propogules, lower levels of endemism, and lack of ownership) and the paucity of available information. The current study aimed to investigate the applicability of systematic approaches to the process of selecting sites for a network of potential replenishment zones for seabream species that could supplement protection already afforded by existing no-fishing reserves. Since many of these seabream species are popular targets in both the recreational and commercial linefishery sectors, they have been overexploited and are in need of additional protection. Information on these species and the diversity of their associated reefs were obtained through consultations with scientists, managers and resource-users (namely SCUBA divers, spearfishers as well as recreational and commercial fishers). These data were obtained during workshops where Participatory Rural Appraisal (PRA) scoring and mapping methods were applied. Although ordinal-scale, rather than interval-or ratio-scale data were obtained, these data could be used in an interactive selection process. Because these methods require relatively cheap materials and few personnel, they could be used to collect information where limited budgets are available. Quantitative targets for the protection of individual species were set on the basis of their status in the Marine Living Resource Act, since this reflected their different requirements for protection. A preliminary investigation indicated that the current no-fishing reserves effectively achieved most of these goals for seabream species. The selection of sites for the replenishment network was based on irreplaceability analyses, while decisions between sites with lower irreplaceability values were based on explicit design rules. A total of 26 sites were required to achieve targets for all species. These replenishment zones could potentially be established, managed and monitored by voluntary community groups. This study therefore indicated that systematic conservation planning can successfully be applied to the marine environment, while the involvement of stakeholders is crucial to ensure that conservation action is supported.
25
Pankhurst, Patricia Melva. "Growth, development and visual ontogeny of two temperate reef teleosts Pagrus auratus, (Sparidae) and Forsterygion varium, (Tripterygiidae)." Thesis, University of Auckland, 1991. http://hdl.handle.net/2292/2000.
Abstract:
Growth, development and behaviour were examined in artificially reared larval Pagrus auratus and Forsterygion varium, from the time of hatching. Yolk-sac larval P.auratus hatched at a small size (2.00mm SL), without functional eyes, mouth or digestive tract, and for three days spent long periods at rest. Growth was initially rapid but slowed by 3 days as yolk reserves neared depletion. By days 4-5, the mouth had opened, eyes were functional, yolk was depleted, and a rudimentary gut had formed. Larvae were now able to maintain a horizontal swimming mode and were actively searching for and attacking prey. First feeding was observed in some larvae. Growth was retarded during the transition from endogenous to exogenous nutrition and then increased as feeding proficiency improved. Yolk-sac F.varium hatched at a larger size (4.78mm SL), with functional eyes and jaws. Larvae were able to maintain a horizontal swimming mode from hatching. First feeding was observed from the first day after hatching. F.varium larvae grew steadily from the time of hatching. Ocular morphology was examined in larval, juvenile and adult P.auratus and F.varium. There was a 96 fold increase in eye size, from 0.23mm diameter in a 4 day old larval P.auratus (3.4mm SL) to a maximum diameter of 22mm in an adult of 333mm body length. F.varium displayed a 26 fold increase in eye size, from 0.28mm diameter in the smallest larva (5.00mm SL) to a maximum eye diameter of 7.2mm in a 11gmm long adult. Larval fish had pure cone retinae, however putative rod precursor cells were present from hatching in F.varium and from 18 days in P.auratus. Juvenile and adult fish had duplex retinae with cones arranged in a square mosaic in which 4 twin cones surround a central single cone. Hypertrophy of cone ellipsoids with increasing eye size, resulted in maintenance of a closely packed array in fishes of all sizes. The appearance of retinomotor movements was coincident with the development of a duplex retina in both species. Theoretical spatial acuity (calculated as a function of cone spacing and focal length of the lens) was poor in the smallest larval fish (2° 1' and 1° 8' minimum separable angle in 4 and 1 day old P.auratus and F.varium respectively) but improved to asymptotic values in adults (3'- 4', and 9' in P.auratus and F.varium respectively). Behavioural acuity (determined using the optokinetic response) of 4 day old larval P.auratus (37° 30') and 1 day old F.varium (29°) was very much lower than histological estimates. Behavioural acuity improved to 8° 8' in 16 day old P.auratus and 4° 18' in 14 day old F.varium, but did not attain theoretical estimates for fish of that size (55' and 54'). A rudimentary retractor lentis muscle was first apparent in larval fish 1 week after hatching, and was coincident with the formation of a posterior lental space. Presumably larval fish eyes were incapable of accomodative lens movements until this time. A relative measure of Matthiessen's ratio (distance from lens centre to boundary of the pigmented retinal epithelium/lens radius) measured histologically, decreased from 4.2 and 2.7 in 3 day old P.auratus and newly hatched F.varium, to 2.2 and 2.3 in larvae 22 and 16 days of age respectively. This suggests that growth of the retina and lens were not symmetrical in the eyes of very small larval fish. If Matthiessen's ratio holds for little eyes, then they will initially be strongly myopic. This may account in part for the mismatch between behavioural and theoretical acuity. Perceptive distances of first feeding larval P.auratus and F.varium, estimated for prey items equal in dimensions to maximum jaw widths, were very small (0.2mm and 0.4mm for prey 0.15mm and 0.2mm in size respectively), but increased with increasing body size to 2.1mm and 4.0mm for prey 0.3mm in size, at 16 and 14 days of age respectively. These data have implications for larval feeding in the wild.
26
Desdevises, Yves. "Recherche des déterminants de la spécifité parasitaire dans le modèle Lamellodiscus (Diplectanidae, Monogenea)-Sparidae (Teleostei) en Méditerranée." Perpignan, 2000. http://www.theses.fr/2001PERP0445.
Abstract:
L'objectif de cette thèse était de mieux comprendre ce qui contrôle la spécifité parasitaire dan sle système hôte-parasite constitué par les poissons de la famille Sparidae et leurs monogènes (Plathelminthes ectoparasites) spécifiques du genre Lamellodiscus. Il s'agissait de comprendre les causes amenant une espèce parasite à utiliser une seule ou plusieurs espèces hôtes. L'hypothèse d'une augmentation de la diversité taxonomique avec la spécifité a également été testée. La coévolution hôte-parasite a été étudiée afin de déterminer si le profil d'association hôte-parasite est contrôlé par des interactions coévolutives. Des phylogénies ont été élaborées pour les hôtes et les parasites à partir de données moléculaires obtenues par séquençage d'ADN. Cette analyse a permis de reconsidérer le statut taxonomique de plusieurs spèces de monogènes. Une méthode de étude de la coévolution, ParaFit, a été mise au point pendant la thèse. Ce système ne semble pratiquement pas être soumis à des phenomènes de cospéciation. Aucun lien entre la diversifictaion taxonomique et la spécifité n'a puêtre mis en évidence chez les Lamellodiscus et la famille qui le contien, les Diplectanidae. Un te lien a été mis en évidence au niveau des groupes principaux de parasites. Les déterminants écologiques et phylogénétiques de la spécifité ont ensuite été recherchés à l'aide d'analyses statistiques multivariables. Les variables considérées étaient des caracteristiques des hôtes considérés comme des determinants écologiques potentiels de la spécifité. La phylogénie des parasites a été prsie en compte dans ces analyse à l'aide de méthodes comparatives. La spécifité apparaît être fortement contrainte par la phylogénie, ce qui suggère l'existence de déterminants génétiquement transmissibles. Les analyse révèlent également que les parsites spécialistesont tendance à utiliser les hôtes les plus grands. Cela est interprété comme une spécialisation sur une ressource prédictibleThe objective of this thesis was to obtein a better understanding of the factors controlling host specifity in the host-parasite system formed by fish from the family Sparidae and their specifique monogeneans parasites from the genus Lamellodiscus (Platyhelminthes)
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Accioly, Ingrid Vilar. "Levantamento cariot?pico em esp?cies de peixes marinhos costeiros de fundo arenoso (Osteichthypes, Perciformes)." Universidade Federal do Rio Grande do Norte, 2007. http://repositorio.ufrn.br:8080/jspui/handle/123456789/16774.
Abstract:
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Previous issue date: 2007-02-27Cytogenetics analyses in fish are important because they compose a private group among the vertebrates, occupying a central position in the animal evolution. The Perciforms Order, dominant in the marine and freshwater environment, it constitutes a model potentially useful in the genetic evaluation of populations, as well as in the understanding of its evolutionary processes. In spite of this, cytogenetics studies in this great group is scarce, above all for the inhabitants of sandy bottom and pelagics habits. The present work proposed to contribute for the cytogenetic characterization of nine species of fish marine of sandy bottom of the coast of Rio Grande do Norte (Brazil), identifying the evolutionary patterns related to the karyotype in these species and the existence of filogenetics affinities between them and other Perciformes. The animals were collected in the beaches of the Redinha, Ponta Negra and B?zios (Coast of Rio Grande do Norte) and in Saint Peter and Saint Paul Archipelago. Later on they were submitted to the cytogenetics technical that consist of mitotic estimulation, obtaining of mitotics chromosomes, proceeded by techniques of conventional coloration (Giemsa) and chromosomic bands (Ag-RONs and C band). Diploid number and fundamental number equal to 48 were observed in most of the species: Menticirrhus americanus, Ophioscion punctatissimus, Pareques acuminatus (Sciaenidae); Chloroscombrus chrysurus (Carangidae); Echeneis sp. 2 (Echeneidae); Archosargus probatocephalus (Sparidae) and Orthopristis ruber (Haemulidae). Trachinotus goodei (NF=52) (Carangidae) and Echeneis sp. 1 (Echeneidae) (NF=54) presented variation in NF, staying constant a diploid number equal to 48. RONs was situated in pericentromeric position in whole the scianids, and in the species Echeneis sp. 2 (22? pair), O. ruber and A. probatocephalus (1? pair), coinciding with great heterocromatics blocks in M. americanus (1? pair), P. acuminatus (2? pairl) and O. ruber (1? pair). RONs was also located in the telomeric area of the short arm of the 5? and 11? acrocentrics pairs in T. goodei, 4? and 19? pairs of C. chrysurus, 1? pair (sm) of Echeneis sp. 1. The C band detected centromeric blocks in most of the chromosomes of the species of Sciaenidae, Carangidae and Echeneidae, with great blocks in A. probatocephalus (4? pair). Heterocromatic blocks in telomeric areas in submetacentrics of Echeneis sp. 1, and pericentromerics in M. americanus (1? and 8? pairs), O. punctatissimus (1? pair) and P. acuminatus (2? pair) were also observed. It is noticed a marked conservatism cromossomic in the species of the family Scianidae and Haemulidae in what says respect to the number of acrocentrics chromosomes and the location of RONs. Even so it is outstanding the presence of heterocromatinization events during the karyotypic evolution of this family. Already in the families Sparidae and Carangidae, the obtained results reaffirm examples of small variations structural resultants of inversion and translocation Robertsonian, as important mechanisms of diversification karyotipical, as well as a pattern numerical evolutionary conserved, also observed in representatives of Echeneidae of Atlantic in relation to Pacific. The presence of RONs multiple, observed in the species T. goodei and C. chrysurus seems to represent a character derived in the family Carangidae. The results for the species O. ruber and A. probatocephalus suggest the presence of possible geographical or climatic barriers among populations of NE of Brazil in relationship the one of the SE
An?lises citogen?ticas em peixes s?o importantes porque os mesmos comp?em um grupo particular entre os vertebrados, ocupando posi??o central na evolu??o animal. A Ordem Perciformes, dominante nos ambientes marinhos e dulc?colas, constitui um modelo potencialmente ?til na avalia??o gen?tica de popula??es, como tamb?m no entendimento de seus processos evolutivos. Apesar disto, ainda s?o escassos os estudos citogen?ticos neste grande grupo, sobretudo para os habitantes de fundo arenoso e h?bitos pel?gicos. O presente trabalho se prop?s a contribuir para a caracteriza??o citogen?tica de nove esp?cies de peixes marinhos litor?neos de fundo arenoso do litoral do Rio Grande do Norte (Brasil), identificando os padr?es evolutivos relacionados ao cari?tipo nestas esp?cies e a exist?ncia de afinidades filogen?ticas entre elas e outros Perciformes. Os animais foram coletados nas praias da Redinha, Ponta Negra e B?zios (Litoral do Rio Grande do Norte) e no Arquip?lago de S?o Pedro e S?o Paulo. Posteriormente foram submetidos ?s t?cnicas citogen?ticas que consistem em estimula??o mit?tica, obten??o de cromossomos mit?ticos, seguida por t?cnicas de colora??o convencional (Giemsa) e bandamentos cromoss?micos (Ag-RONs e bandamento C). N?mero dipl?ide e n?mero fundamental iguais a 48 foram observados na maioria das esp?cies: Menticirrhus americanus, Ophioscion punctatissimus, Pareques acuminatus (Sciaenidae); Chloroscombrus chrysurus (Carangidae); Echeneis sp. 2 (Echeneidae); Archosargus probatocephalus (Sparidae) e Orthopristis ruber (Haemulidae). Trachinotus goodei (NF=52) (Carangidae) e Echeneis sp. 1 (Echeneidae) (NF=54) apresentaram uma varia??o no NF, mantendo-se constante um n?mero dipl?ide igual a 48. As RONs estavam situadas em posi??o pericentrom?rica em todas os scian?deos, e nas esp?cies Echeneis sp. 2 (22? par), O. ruber e A. probatocephalus (1? par), coincidindo com grandes blocos heterocrom?ticos em M. americanus (1? par), P. acuminatus (2? par) e O. ruber (1? par). As RONs tamb?m foram localizadas na regi?o telom?rica do bra?o curto do 5? e 11? pares acroc?ntricos em T. goodei, 4? e 19? pares de C. chrysurus, 1? par (sm) de Echeneis sp. 1. O bandamento C detectou blocos centrom?ricos na maioria dos cromossomos das esp?cies de Sciaenidae, Carangidae e Echeneidae, com grandes blocos em A. probatocephalus (4? par). Blocos heterocrom?ticos em regi?es telom?ricas em submetac?ntricos de Echeneis sp. 1, e pericentrom?ricas em M. americanus (1? e 8? pares), O. punctatissimus (1? par) e P. acuminatus (2? par) tamb?m foram observados. Nota-se um marcante conservadorismo cromoss?mico nas esp?cies da fam?lia Scianidae e Haemulidae no que diz respeito ao n?mero de cromossomos acroc?ntricos e a localiza??o das RONs. Por?m ? destacada a presen?a de eventos de heterocromatiniza??o durante a evolu??o cariot?pica desta fam?lia. J? nas fam?lias Sparidae e Carangidae, os resultados obtidos reafirmam exemplos de pequenas varia??es estruturais resultantes de invers?es e transloca??es Robertsonianas, como principais mecanismos de diversifica??o cariot?pica, bem como um padr?o evolutivo mais conservado numericamente, tamb?m observado em representantes de Echeneidae do Atl?ntico em rela??o ao Pac?fico. A presen?a de RONs m?ltiplas, observadas nas esp?cies T. goodei e C. chrysurus parecem representar um car?ter derivado na fam?lia Carangidae. Os resultados para as esp?cies O. ruber e A. probatocephalus sugerem a presen?a de poss?veis barreiras geogr?ficas ou clim?ticas entre suas popula??es no NE do Brasil, quando comparada com a regi?o SE
28
李景耀 and King-yiu Lee. "Molecular cloning and characterization of gonadotropin-releasing hormone receptors in the black seabream (Mylio macrocephalus)." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31224635.
29
Watt-Pringle, Peter Andrew. "Movement bahaviour of three South African inshore sparid species in rocky intertidal and shallow subtidal habitats." Thesis, Rhodes University, 2009. http://hdl.handle.net/10962/d1005147.
Abstract:
This study investigated the movement behaviour of three inshore South African sparids – blacktail (Diplodus sargus capensis), zebra (Diplodus cervinus hottentotus) and white musselcracker (Sparodon durbanensis), popular inshore fishery species caught in appreciable numbers along much of the South African coast. The first study component examined movements of juveniles in a rocky intertidal nursery area at Schoenmakerskop near Port Elizabeth. Juveniles in a single gully were tagged with Visible Implant Elastomer (VIE) and resighted at the study site on snorkelling gear over a seven-month period. Tagged zebra and musselcracker displayed limited movement between potential low tide refuges, being observed repeatedly in the same gully over the full duration of the study. However, blacktail displayed greater movements and were seen infrequently in the later period of the study, probably having undergone an ontogenetic habitat shift to subtidal areas. There was evidence that blacktail maintain use of their intertidal nursery over high tide, during which the other two species moved into shallower areas adjacent to their low tide refuge. The results of three national tagging programs were analysed to determine the movement patterns of adolescent and adult fishes. The coast-wide ORI-WWF National Voluntary Tagging Program and two dedicated research programs in marine protected areas (MPAs) at De Hoop MPA and Tsitsikamma National Park (TNP) recorded few large-scale movements of tagged adult blacktail, zebra and juvenile musselcracker. High spatial-resolution data from the TNP suggested movements were usually on scales far smaller than one km. Together with long periods at liberty for many recaptured individuals, this suggests these fishes are longterm residents of small home range areas. However, tagged musselcracker over 600 mm forklength (adults) were observed to make large-scale movements, including some in excess of 800 km from Eastern Cape to KwaZulu-Natal waters. Predominantly eastward movements of adults recaptured during the spawning season indicate seasonal spawning migrations that occur in different regions of the coast. These enable the use of prevailing oceanographic currents to disperse eggs and larvae to suitable rocky nursery habitat. The third component of this study made use of high-resolution data on the temporal and spatial distribution of catches by scientific angling in the TNP to examine the daily activity patterns of the study species in relation to diel and tidal cycles, and habitat use. Blacktail capture probability was correlated with the diurnal light cycle, with peaks close to twilight suggesting elevated crepuscular foraging activity. Catches of blacktail, zebra and small musselcracker were correlated with the tidal cycle, foraging peaking over high tide periods. All three species used shallow inshore habitats extensively for foraging, blacktail showing a preference for sandy areas, while zebra and small musselcracker preferred shallow reef. Capture probability of larger musselcracker, however, was unrelated to habitat, possibly evidence of increasing area and habitat use with an ontogenetic change in diet. The lifetime movement patterns of these three species are discussed in relation to conservation measures and their management in South African fisheries. Restricted movement throughout post-settlement life for blacktail and zebra, and during the juvenile phase for musselcracker, makes local populations vulnerable to overexploitation. At present, MPAs probably play an important role in protecting local blacktail and zebra populations from overexploitation, and limited post-settlement movements mean the degree of larval dispersal between protected and adjacent areas will likely determine the effectiveness of MPAs in enhancing fisheries for these species. By contrast, MPAs likely provide recruits to fisheries for musselcracker during ontogenetic movements and dispersal from MPAs during spawning migrations. MPAs only offer partial protection to adult musselcracker populations in the spawning season, but this could nevertheless be significant under high levels of exploitation.
30
Vigliola, Laurent. "Contrôle et régulation du recrutement des Sparidae (Poissons, Téléostéens) en Méditerranée : importance des processus pré- et post-installation benthique." Aix-Marseille 2, 1998. http://www.theses.fr/1998AIX22082.
Abstract:
La population constitue la piece structurale elementaire des ecosystemes. La taille des populations d'organismes marins benthiques a phase larvaire planctonique etant determinee en quasi-totalite par l'intensite du recrutement, parametre repute pour sa variabilite et son caractere imprevisible, il est necessaire d'en etudier precisement les modalites. Ce travail de quatre annees (1993 a 1996) porte sur l'importance des processus pre- et post-installation benthique sur le recrutement de trois especes de poissons sparidae des cotes rocheuses mediterraneennes, diplodus puntazzo (cetti), d. Sargus (l. ) et d. Vulgaris (geoffroy saint-hilaire). Les caracteristiques demographiques de ces especes ont ete etudiees entre l'installation benthique des larves dans les criques rocheuses peu profondes du golfe de marseille (43 10'n, 5 20'e) et le recrutement des juveniles dans les populations d'adultes. Deux techniques d'etude ont ete utilisees : l'analyse otolithometrique et les recensements visuels. Pour les trois especes de diplodus, l'utilisation conjointe de ces deux techniques a permis d'estimer les durees de vie larvaire planctonique, de determiner les periodes d'installation benthique et de recrutement, de relier l'intensite de l'installation benthique aux facteurs climatiques impliques dans le transport larvaire, d'estimer les taux de croissance et de mortalite tout en developpant des modeles mathematiques explicatifs et novateurs, et de preciser la biologie et l'ecologie de ces poissons durant cette phase critique de leur cycle de vie. Finalement, la variabilite du recrutement de ces trois especes de diplodus a ete expliquee, ses causes isolees, et les effets relatifs des differents facteurs responsables quantifies. L'intensite du recrutement des diplodus depend de l'intensite de l'installation, i. E. De l'apport larvaire, de la croissance et de la mortalite benthique. L'intensite de l'installation benthique varie entre les especes d'un facteur 3 a 100 en liaison avec la taille des stocks de geniteurs. Chez une meme espece, l'apport larvaire varie d'un facteur 4 a 6 en fonction de l'intensite des vents impliques dans le retour des larves planctoniques a la cote. Cette variabilite de l'apport larvaire modifie le niveau du recrutement par un facteur 2 a 3. La croissance benthique depend de la temperature de l'eau et ses variations modifient le recrutement des diplodus par un facteur 2 a 5. La mortalite benthique est tres elevee, 43 a 99% suivant les especes, et a ete expliquee par la predation. Cette mortalite est denso-dependante, ce qui a pour effet de reguler le recrutement des diplodus en divisant par un facteur 2 la variabilite initiale de l'apport larvaire. Les implications de ce travail en dynamique des populations, en biogeographie et en ecologie evolutive sont discutees.
31
Pulfrich, Andrea Christine. "Aspects of the biology of, and fishery for, the Hottentot, Pachymetopon blochii (Val.) (Sparidae), in the Western and Southwestern Cape." Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/21932.
Abstract:
Data extracted from historic records have been used together with information collected during a survey of major fishing centres in the west and southwest Cape, from Port Nolloth to Struis Bay, to document the development of the handline fishery, with special reference to the fishery for hottentot Pachymetopon blochii (Val.). The fishing communities are described and social conditions are compared with those reported in earlier surveys. Changes in the fishing vessels and tackle used in the handline fishery are described and the economic status of the fishery evaluated. The distribution and availability of P. blochii are assessed in relation to the various tackle types and catch methods in different areas and the contribution by this species to the total annual linefish catch is estimated. Total fishing effort expended in the commercial linefishery is used to calculate catch-per-unit-effort indices for the hottentot fishery and the seasonal and long-term trends in these indices are evaluated in relation to past and present constraints on the marketing of this species.
32
Rosecchi, Elisabeth. "Ethologie alimentaire des Sparidae Diplodus annularis, Diplodus sargus, Diplodus vulgaris, Pagellus erythrinus, Sparus aurata du golfe du Lion et des étangs palavasiens." Montpellier 2, 1985. http://www.theses.fr/1985MON20055.
Abstract:
Le regime alimentaire des spares, de la daurade et du pageot et son role dans le determinisme des migrations entre mer et lagune sont aborbes sous les angles suivants: adaptations morphologiques, choix trophiques, traitement des donnees
33
Leslie, Timothy David. "Assessing estuarine nursery habitats for Cape Stumpnose (Rhabdosargus holubi), (Pisces: Sparidae) in a warm-temperate estuary in the Eastern Cape, South Africa." Thesis, Rhodes University, 2016. http://hdl.handle.net/10962/3178.
Abstract:
The nursery role hypothesis provides an approach for assessing the nursery function of habitat types within estuaries. This study attempted to assess the nursery value of the dominant estuarine habitats in the Bushmans Estuary for Rhabdosargus holubi (Steindachner 1881) by analysing habitat complexity, relative abundance and behaviour of R. holubi and using stomach contents analysis and dietary diatom composition as indicative of feeding habitat. Structural habitat complexity was assessed in Zostera capensis (Setchell) seagrass and Spartina maritima (Curtis Fernald) salt marsh by sampling above-ground stem density and length, and total cover per unit area (Ct/At). Dimensionless habitat complexity indices such as the interstitial spatial index (ISI) at three magnifications and fractal geometry at two magnifications were used to further analyse habitat complexity. Above-ground biomass (P<0.05) in each season and canopy height (P<0.001) were significantly higher in salt marsh than in seagrass whilst stem density was significantly higher in seagrass than in salt marsh in each season (P<0.001). Each dimensionless index indicated that complexity is notably higher in seagrass than in the salt marsh. Using dimensionless indices that analyse complexity at different spatial scales provided a better analysis of habitat complexity than canopy height and biomass as it allowed for direct comparisons between habitat types. Underwater video cameras were deployed in seagrass, salt marsh and sand flat habitats to assess the relative abundance and behaviour of R. holubi. The relative abundance of R. holubi was significantly higher in seagrass than salt marsh and sand flats, whilst the behaviour of R. holubi indicated a high degree of habitat use in structured habitats and a low degree of habitat use in unstructured sand flat habitats. This indicated that not only are juvenile R. holubi a vegetation-associated species, but also a species that prefers seagrass to salt marsh.
34
Clarke, John Ross. "Aspects of the biology of the musselcracker, Sparodon Durbanensis, and the bronze bream, Pachymetopon grande, (Pisces : Sparidae), with notes on the Eastern Cape recreational rock-angling and spear fisheries." Thesis, Rhodes University, 1988. http://hdl.handle.net/10962/d1001966.
Abstract:
The musselcracker, Soarodon durbanensis, and the bronze bream, Pachymetopon arande, are important components of rock-angling and spearfishing catches In the Eastern Cape. Aspects of their biology, including age and growth, reproduction, nursery areas and feeding, were Investigated to provide a basis for the rational exploitation of the resource. Both species are slow-growing and long-lived. Growth in S. durbanensls was described by the von Bertalanffy growth equation: Lt(mm) = 1021.2(1-e⁻°.°⁹°°⁽t ⁻° .⁷°⁹⁾). The von Bertalanffy growth model did not describe the total data set in P. grande, but by excluding the zero and one year old fish the data were described by: Lt(mm) = 461.1(1-e⁻°.¹⁵³⁽t ⁺¹.⁶⁴°⁾). Detailed histological examination of gonadal development showed that S. durbanensis and P. grande are rudimentary hermaphrodites. Both species had restricted breeding seasons which coincided with peak exploitation. Results indicated that both species are group spawners with pelagic eggs. Size at 50% maturity in S. durbanensis and P. grande was determined at 350 and 300mm fork length, respectively, corresponding to ages of 4.5 and 5.5 years. Intertidal pools functioned as nursery areas for S. durbanensis during the first year, whereas subtidal waters were more important for larger juveniles. P. grande juveniles were commonly observed on subtidal weed beds to a depth of 10m. A size-related change in the diet of S. durbanensis was observed. The juveniles were omnivorous, feeding predominantly on gastropods, echinoids and chlorophytes. The adults fed on a variety of large, reef-associated invertebrates. P. grande were omnivorous, with macroalgae being the principal dietary component. This species appears to utilise the storage and extracellular carbohydrates of the macroalgae. Results showed that macroalgal degradation by gut endosymbionts and the utilisation of macroalgal epibionts does not appear to occur in this species. A detailed analysis of catch composition and catch per unit of effort In the Port Elizabeth rock-angling fishery and the Eastern Cape spearfishery emphasised the recreational importance of S. durbanensis and P. grande. The localised distribution, slow growth and late maturation in both species results in their being susceptible to over-exploitation in these size-selective fisheries. Current legislation protecting these fish is discussed in relation to the findings of this study and additional management measures are proposed.
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Pérez-del-Olmo, Ana. "Biodiversity and structure of parasite communities in Boops boops (Teleostei: Sparidae) from the Western Mediterranean and off the North East Atlantic coasts of Spain." Doctoral thesis, Universitat de València, 2008. http://hdl.handle.net/10803/10353.
Abstract:
The present study carried out a detailed assessment of the metazoan parasite fauna in Boops boops (Sparidae) along the Spanish coasts off the Western Mediterranean and North-East Atlantic, which provided taxonomically consistent dataset comprising three levels of parasite community organisation that allowed questions regarding the structure of parasite communities to be addressed.The diversity of the parasite fauna of B. boops appeared to be higher than previously thought, as evidenced by the description of one new species, Wardula bartolii Pérez-del-Olmo et al., 2006 and the recovery of 53 parasite species (25 new host records). The complete checklist of parasites of this host throughout its distributional range comprises 78 species and 365 host-parasite-area records. A group of nine species with a wide geographical distribution was identified as the core of the parasite fauna of B. boops. The regional parasite fauna of B. boops was richest in the North-East Atlantic. There was a clear separation of the North-East Atlantic and Mediterranean local faunas, with a 'transition' location occupying an intermediate position. Local parasite faunas were generally diverse. There was a high representation of parasites with complex life-cycles, transmitted via food ingestion, mostly trematodes. The phylogenetic influence on the parasite communities in B. boops is rather weak, since generalist parasites comprised a considerable part of communities. The species of the core parasite fauna of B. boops were already present in juvenile fish, whereas all species added to communities in larger fish were rare/accidental. The observed sequence of species appearance and persistence supported the hypothesis that species with wide geographical distributions appear in the fish population earlier than rare/stochastic species. Parasite communities were rich and abundant from an early age. Six species of the core parasite fauna of B. boops were identified as key parasites in developing communities since they persisted as common in all size cohorts and represented the majority of the individuals. A nested subset pattern was found which could not be completely attributed to either accumulation over time or segregation of the parasite species among different host cohorts. Nestedness was strongly related to the differential species abundance, suggesting that passive sampling could be the mechanism leading to this non-random structure.The data revealed that the geographical distance and the region affect the species composition and structure of parasite faunas and component communities in B. boops. The distance between localities/regions contributed significantly to the decay of the similarity estimated from parasite abundance at the infracommunity level. The structured spatial patterns were consistent in time but not across seasons. The spatial synchrony observed was solely due to the assemblage of the 'core' species, supporting the hypothesis that widespread species would be strongly associated with patterns of variation in environmental conditions. The interspecific abundance-distribution patterns were recognized as the most important for the distance-decay relationship of similarity in this system due to the strong correlations observed at all scales of analysis.The comparative analyses revealed a notable alteration of parasite abundance patterns and dramatic changes in community richness, abundance and structure of parasite communities in B. boops studied after the Prestige oil-spill. A directional trend in parasite community succession was detected. However, the differences were still large indicating that shifting pollution baselines probably affect community recovery.The elevated levels of monoxenous infections could indicate that changes in immune parameters of fish. The increase of heteroxenous may have reflected an enhancement of the populations of the mollusc and copepod hosts due to organic enrichment following the oil-spill. Focusing on higher taxonomic/functional levels and the use of multivariate statistical approach have proved to be very useful in studying the response of parasite communities to pollution.En la presente tesis doctoral se realizó un estudio exhaustivo de los metazoos parásitos de la boga, Boops boops (Sparidae) en la costa Mediterránea y Atlántica española. La diversidad parásita fue mucho mayor de lo que previamente se pensaba, como se evidenció en la descripción de una nueva especie y la presencia de 53 especies (incluyendo 25 nuevos registros). Se encontró regularmente un grupo de nueve especies de amplia distribución, que fueron considerados el núcleo de la parasitofauna de B. boops. Las faunas parásitas locales resultaron ser diversas y caracterizadas por una gran representación de parásitos generalistas y con ciclos vitales complejos. La secuencia de aparición y persistencia observada en el desarrollo de las comunidades parásitas apoyó la hipótesis de que las especies con distribución geográfica amplia aparecen en las poblaciones de peces antes que las raras y estocásticas. Las comunidades parásitas de B. boops fueron ricas y abundantes desde una edad temprana. Se detectó una estructura anidada fuertemente relacionada con una abundancia diferencial de las especies, sugiriendo que el muestreo pasivo de parásitos del hospedador podría ser el mecanismo responsable de esta estructura no-aleatoria. Tanto la distancia geográfica como la región de origen afectaron la composición de especies y la estructura de las faunas parásitas y comunidades componentes. El patrón de estructura espacial fue consistente en el tiempo pero no entre estaciones. La relación abundancia-distribución interespecífica fue el aspecto más importante en el declive de la similitud con la distancia.El análisis comparativo de las muestras de localidades afectadas por el vertido del petrolero "Prestige reveló un cambio drástico en la riqueza, abundancia y estructura de las comunidades parásitas, así como una notable alteración de los patrones de abundancia. Se detectó una tendencia direccional en la sucesión de las comunidades parásitas tras el vertido. Sin embargo, las diferencias siguen siendo acusadas, lo que podría indicar un desplazamiento de los niveles base que estaría afectando la recuperación de las comunidades bentónicas y parásitas tras el vertido. Tanto el enfoque basado en niveles taxonómicos y funcionales superiores como la aproximación mediante análisis estadísticos multivariantes, resultaron ser muy efectivos para este tipo de estudios.
36
Al-Abdul-Elah, Khaled M. "Biotic and abiotic factors influencing initial swimbladder inflation of the blue-finned sea bream Acanthopagrus cuvieri (Sparidae), with particular reference to aquaculture in Kuwait." Thesis, University of Stirling, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278746.
37
Coco, Salvatore. "Ritmi stagionali negli Sparidi: 3 anni di video monitoraggio con l’osservatorio cablato OBSEA." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
Abstract:
In questo studio è stato utilizzato un osservatorio video cablato (OBSEA, www.obsea.es) per il monitoraggio dei ritmi stagionale e annuali della composizione della comunità ittica costiera (20 m) nel Mediterraneo occidentale, in prossimità di una struttura artificiale. Nell’arco di 3 anni (2012-2014) è stata scattata una foto ogni 30 minuti utilizzando una videocamera ad alta risoluzione. Sono state inoltre registrate due importanti variabili ambientali che modulano il comportamento dei pesci: la temperatura dell'acqua e il fotoperiodo. In ogni foto è stato determinato il numero di individui di 6 specie appartenenti alla famiglia degli Sparidi: Dentex dentex, Diplodus sargus, Diplodus vulgaris, Diplodus puntazzo, Diplodus annularis, Diplodus cervinus. La ritmicità delle serie temporali è stata studiata utilizzando il linguaggio di computazione R attraverso uno dei suoi pacchetti aggiuntivi, RAIN. Inoltre, per evidenziare eventuali correlazioni tra le variabili scelte e le specie prese in esame sono state effettuate analisi di correlazione utilizzando il coefficiente per ranghi di Spearman. I risultati indicano che le specie D. dentex, D. sargus, D. annulars, D. vulgaris presentano una ritmicità annuale nella loro abbondanza presso la barriera artificiale. Dall’analisi di correlazione per ranghi di Spearman è stato osservato che la specie D. dentex presenta una correlazione positiva con entrambe le variabili ambientali. Le specie D. sargus e D. vulgaris presentano una correlazione positiva con la temperatura dell’acqua e nessuna correlazione con il fotoperiodo. Il D. annularis presenta una correlazione negativa con entrambe le variabili. Le specie D. puntazzo e D. cervinus non presentano nessuna correlazione con entrambe le variabili. La piattaforma OBSEA ha permesso di eseguire uno studio completo ed ha evidenziato le differenze ecologiche delle specie prese in esame, senza creare perturbazioni associate al campionamento.
38
Arendse, Clement J. "Aspects of the early life history and a per-recruit assessment of white stumpnose Rhabdosargus globiceps (Pisces: Sparidae) in Saldanha Bay with recommendations for future research and monitoring." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/10069.
Abstract:
This study focuses on several aspects of the life history of R. globiceps, and includes a study of juvenile habitat, a hatch date analysis, methods to increase precision of age estimates obtained from reading otoliths and a per-recruit assessment.
39
Baelde, Pascale. "La Faune ichtyologique du Lagon du Grand Cul-de-SacMarin en Guadeloupe structure des peuplements et contribution à l'étude de la biologie d'Archosargus rhomboïdalis, Sparidae, et d'Ocyurus chrysurus, Lutjanidae." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37595657w.
40
Murray, Taryn Sara. "Movement patterns and genetic stock delineation of an endemic South African sparid, the Poenskop, Cymatoceps nasutus (Castelnau, 1861)." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001514.
Abstract:
Poenskop Cymatoceps nasutus (Pisces: Sparidae), an endemic South African sparid, is an important angling species being predominantly targeted by the recreational shore and skiboat sector. This species is slow-growing, long-lived, late-maturing and sex-changing, making poenskop acutely sensitive to over-exploitation. Despite interventions, such as the imposition of size and bag limits (currently 50 cm TL and one per licensed fisher per day) by authorities, catch-per-unit-effort trends reflect a severe and consistent stock decline over the last two decades. Poenskop has been identified as a priority species for research and conservation. Although the biology and population dynamics of this species have been well-documented, little is known about the movement behaviour of poenskop. Furthermore, there is a complete lack of information on its genetic stock structure. This thesis aimed to address the current knowledge gaps concerning movement behaviour and genetic stock structure of poenskop, making use of a range of methods and drawing on available information, including available fishery records as well as published and unpublished survey and research data, and data from long-term monitoring programmes. Analysis of available catch data (published and unpublished) revealed a decline in the number of poenskop caught as well as size of fish taken over the last two decades, ultimately reflecting the collapse of the stock (estimated to be at 20% of their pristine level). Improved catch-per-unit-effort data from the Tsitsikamma National Park Marine Protected Area (MPA), and larger poenskop being caught in the no-take areas than adjacent exploited areas of the Pondoland MPA confirmed that MPAs can be effective for the protection and management of poenskop. The current MPA network in South Africa is already wellestablished, and encompasses considerable reef areas, being preferable for poenskop habitation. Conventional dart tagging and recapture information from three ongoing, long-term fishtagging projects, conducted throughout the poenskop’s distribution, indicated high levels of residency at all life-history stages. Coastal region, seasonality and time at recapture did not appear to have a significant effect on the level of movement or distance moved. However, on examining the relationship among coastal movements and fish size and ages, larger and older fish (adults) moved greater distances, with juveniles and sub-adults showing high degrees of residency. An estimation of home-range size indicated smaller poenskop to hold smaller home-ranges, while larger poenskop hold larger home-ranges. Large easterly displacements of a number of adult poenskop is in accordance with previous findings that this species may undertake a unidirectional migration up the coastline of South Africa where they possibly settle in Transkei waters for the remainder of their lives. This high level of residency makes poenskop vulnerable to localised depletion, although they can be effectively protected by suitable MPAs. Despite considerable tagging effort along the South African coastline (2 704 poenskop tagged with 189 recaptures, between 1984 and 2010), there remains limited information on the connectivity of different regions along the South African coastline. This was addressed using mitochondrial DNA sequencing. The mitochondrial DNA control region was used due to its high substitution rate, haploid nature, maternal inheritance and absence of recombination. The mtDNA sequencing showed no evidence of major geographic barriers to gene flow in this species. Samples collected throughout the core distribution of poenskop showed high genetic diversity (h = 0.88, π = 0.01), low genetic differentiation among regions, no spatial structure (ɸST = 0.012, p = 0.208) and no evidence of isolation by distance. The collapsed stock status of poenskop as well as the fact that it is being actively targeted by recreational and commercial fishers suggests that this species requires improved management, with consideration given to its life-history style, residency and poor conservation status. Management recommendations for poenskop, combined with increasing South Africa’s existing MPA network, include the possibility of setting up a closed season (during known spawning periods) as well as the decommercialisation of this species. The techniques used and developed in this study can also be adopted for other overexploited linefish species.
41
Duncan, Murray. "The genetic stock structure and distribution of Chrysoblephus Puniceus, a commercially important transboundary linefish species, endemic to the South West Indian Ocean." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1011868.
Abstract:
Chrysoblephus puniceus is an over-exploited linefish species, endemic to the coastlines off southern Mozambique and eastern South Africa. Over-exploitation and habitat loss are two of the biggest threats to the sustainability of fisheries globally. Assessing the genetic stock structure (a prerequisite for effective management) and predicting climate related range changes will provide a better understanding of these threats to C. puniceus which can be used to improve the sustainability of the fishery. Two hundred and eighty four genetic samples were collected from eight sampling sites between Ponta da Barra in Mozambique and Coffee Bay in South Africa. The mitochondrial control region and ten microsatellite loci were amplified to analyse the stock structure of C. puniceus. The majority of microsatellite and mtDNA pairwise population comparisons were not significant (P > 0.05) although Xai Xai and Inhaca populations had some significant population comparisons for mtDNA (P < 0.05). AMOVA did not explain any significant variation at the between groups hierarchical level for any pre-defined groupings except for a mtDNA grouping which separated out Xai Xai and Inhaca from other sampling sites. SAMOVA, isolation by distance tests, structure analysis, principle component analysis and spatial autocorrelation analysis all indicated a single population of C. puniceus as being most likely. The migrate-n analysis provided evidence of current driven larval transport, with net migration rates influenced by current dynamics.Two hundred and thirty six unique presence points of C. puniceus were correlated with seasonal maximum and minimum temperature data and bathymetry to model the current distribution and predict future distribution changes of the species up until 2030. Eight individual species distribution models were developed and combined into a mean ensemble model using the Biomod2 package. Winter minimum temperature was the most important variable in determining models outputs. Overall the ensemble model was accurate with a true skills statistic score of 0.962. Binary transformed mean ensemble models predicted a northern and southern range contraction of C. puniceus' distribution of 15 percent; by 2030. The mean ensemble probability of occurrence models indicated that C. puniceus' abundance is likely to decrease off the southern Mozambique coastline but remain high off KwaZulu-Natal. The results of the genetic analysis support the theory of external recruitment sustaining the KwaZulu Natal fishery for C. puniceus. While the high genetic diversity and connectivity may make C. puniceus more resilient to disturbances, the loss of 15 percent; distribution and 11 percent; genetic diversity by 2030 will increase the species vulnerability. The decrease in abundance of C. puniceus off southern Mozambique together with current widespread exploitation levels could result in the collapse of the fishery. A single transboundary stock of C. puniceus highlights the need for co-management of the species. A combined stock assessment between South Africa and Mozambique and the development of further Marine Protected Areas off southern Mozambique are suggested as management options to minimise the vulnerability of this species.
42
Besseau, Laurence. "L'hermaphrodisme protandre chez les sparidés : les potentialités de l'ovotestis dans le modèle Lithognathus mormyrus." Perpignan, 1991. http://www.theses.fr/1991PERP0114.
Abstract:
L'etude de la sexualite du marbre, lithognathus mormyrus, est apprehendee par une analyse biometrique, sclerochronologique, histologique et cytologique d'une population du littoral mediterraneen roussillonnais. Les parametres de la croissance du marbre sont estimes par ajustement au modele de von bertalanffy. Trois types d'architecture de la sagitta (meb) sont mis en relation avec le statut sexuel des poissons. Les modalites de la gonadogenese chez l. Mormyrus sont decrites: a deux mois, la bisexualite est acquise. Chez des specimens d'un an, trois types d'ovotestis juveniles sont identifies: prevalence testiculaire, equivalence testiculaire et ovarienne, prevalence ovarienne. Les cycles saisonniers de reproduction sont caracterises: repos sexuel d'octobre a mars, gametogenese d'avril a juillet, ponte en aout-septembre et post ponte en septembre. La structure sexuelle de la population est apprehendee par l'analyse de la distribution de frequence de taille, en relation avec le sexe (observations macro- & microscopiques). La moitie seulement de la population est hermaphrodite protandre. 50% des poissons sont gonochoriques secondaires: 40% de femelles primaires et 10% de males persistants. La protandrie n'est donc pas exclusive chez l. Mormyrus. L'inversion sexuelle protandre se realise en 2 etapes (met): 1) l'achevement de l'edification de l'aire ovarienne, durant la phase male fonctionnelle, est un phenomene discontinu, cyclique (en periode post ponte) et discret. 2) la regression du territoire testiculaire, pendant la phase femelle fonctionnelle, est un phenomene continu, qui procede de la degenerescence des spermatogonies, phagocytees par les cellules de sertoli. Des cellules immunitaires interviennent secondairement dans la resorption du materiel male degenerescent, conduisant a la formation de corps bruns (lipofuscines). Les potentialites de l'ovotestis de sparides dans l'expression du sexe sont estimees et discutees
43
Alama, Bermejo Gema. "Parasitological study of cultured and wild sparids in the Mediterranean." Doctoral thesis, Universitat de València, 2011. http://hdl.handle.net/10803/81891.
Abstract:
Aquaculture is a growing agricultural sector that due to the actual market saturation by sea bass and gilthead sea bream, needs for new fish species diversification. Sparid fishes are important candidates for species diversification in the Mediterranean aquaculture. Under culture conditions, parasites may cause serious problems. This thesis aims to improve our knowledge of myxozoan and aporocotylid parasites in sparids which are new candidates or existing Mediterranean aquaculture species. The present study seeks to identify, describe and clarify the taxonomic position of the parasite taxa by morphological and molecular approaches, and by defining their phylogenetical position and relationship with previously described species. Development, habitat selection in the host and pathology are analysed in order to evaluate the pathogenic potential of the parasites described. Also this thesis focuses on the study of parasite life cycles, seasonality, transmission and routes of infection in the fish host, with the final aim to provide information allowing for the development of management strategies for aquaculture systems.
The study led to the following findings and conclusions:
-A new genus and species of blood fluke, Skoulekia meningialis n. gen., n. sp. was described from the common two-banded seabream Diplodus vulgaris in a non common location, the ectomeningeal veins surrounding the optic lobes of the brain. The adults of S. meningialis were found to cause mild, chronic, localised meningitis. Its special location surrounding a vital organ should be kept in mind when establishing D. vulgaris in aquaculture systems.
-Large cysts of myxosporean spores of the species Unicapsula pflugfelderi were detected in the fillets of sand steenbras Lithognathus mormyrus. Myoliquefaction process was not found to occur in U. pflugfelderi. However, the massive presence of macroscopic plasmodia in the fillets of L. mormyrus could produce marketing problems, affecting to the potential of the sand steenbras as an aquaculture candidate.
-A new myxozoan parasite Ceratomyxa puntazzi n. sp. was found to cause histopathological changes in the liver and in the gall bladder of the sharpsnout seabream Diplodus puntazzo and has to be considered as an opportunistic parasite in immunocompromised hosts. The genus Ceratomyxa seems to be very host-specific in sparids and high species diversity can be expected in Mediterranean sparids. The phylogenetical analyses revealed that all ceratomyxid species of sparids from the Mediterranean rise from a common ancestor.
-This thesis provides unique insights into the development and cellular organisation of the myxozoan C. puntazzi. This study is the first use of confocal laser scanning microscopy with specific stains on developmental stages of a myxozoan. C. puntazzi seems to follow a sequence of development with two pathways in the bile: pre-sporogonic proliferative development where stages show high degree of motility, cellular divisions and budding by plasmotomy, and sporogonic development, characterized by the formation and maturation of spores. For the first time in myxozoans, motility and the distribution of potential effectors of motility were analysed. F-actin rich cytoskeletal elements were found to concentrate at one end of the parasite, which produces localised filopodia, thus facilitating parasite motility. The mechanism of budding was identified, for the first time, as an active F-actin dependent separation process.
-Natural exposures of sharpsnout seabream to a C. puntazzi enzootic habitat are the first attempt of conducting a seasonality study in marine myxozoans and provide important insights into the seasonal patterns of myxozoan abundance in a temperate marine environment. C. puntazzi infection in the bile shows a marked temperature-related seasonality, with visual detection of parasites exclusively between April - November. However, PCR detection in the bile is possible all year round. Blood stages were detected all year round by PCR. This indicates that actinospores are present in the sea water and the blood of exposed fish is invaded throughout the whole year. Implications for D. puntazzo culture are discussed.La acuicultura mediterránea necesita diversificación de especies de peces para el cultivo debido a la saturación del mercado con dorada y lubina. En condiciones de cultivo, los peces pueden verse afectados por diversos patógenos, entre ellos los parásitos. Entre los parásitos mas problemáticos en la acuicultura mediterránea, figuran los mixozoos y los aporocotílidos. En esta tesis doctoral se presentan nuevas y se aportan nuevos datos de especies ya descritas de estos dos grupos parásitos, se estudia la relación parasito-hospedador y se incluyen nuevos datos del desarrollo, rutas de infección, ciclo de vida y estacionalidad en especies de peces candidatas para el cultivo. Un nuevo género y especie de aporocotílido Skoulekia meningialis n. gen. n. sp. se halló en un hábitat poco común, las venas ectomeningeales del cerebro de la mojarra Diplodus vulgaris, donde los adultos provocan una meningitis moderada pero crónica. Plasmodios alargados con esporas del mixozoo Unicapsula pflugfelderi se hallaron en la musculatura de la herrera Lithognathus mormyrus y aunque no se observó mioliquefaccion, la presencia masiva de estas estructuras en los filetes puede afectar al potencial de la herrera como especie para la acuicultura. Ceratomyxa puntazzi n. sp. es una nueva especie de mixozoo descrita de la vesícula biliar del sargo picudo Diplodus puntazzo. C. puntazzi provoca cambios histopatológicos en el hígado y la vesícula biliar del sargo picudo y debe considerarse como un patógeno oportunista. C. puntazzi forma parte del complejo de especies del género Ceratomyxa hallado en espáridos del Mediterráneo los cuales provienen de un ancestro común. Dentro del estudio de C. puntazzi, se describen los componentes celulares, y los mecanismos que intervienen en la motilidad de los mixozoos y como estos elementos están implicados en los procesos de gemación y citocinesis en los mixozoos. Experimentos de transmisión con jaulas en el mar a un medio natural enzoótico para C. puntazzi reveló una estacionalidad marcada, con presencia de esporas en la bilis de Abril a Noviembre, pero con detección por PCR durante todo el año tanto en la bilis como en la sangre. Estos resultados tienen implicaciones para el manejo del cultivo del sargo picudo.
44
Romans, Pascal. "Influence et importance relative de facteurs intrinsèques et extrinsèques sur la mortalité des alevins de Sparidés (Pisces) durant la phase d'installation benthique en Méditerranée." Perpignan, 2003. http://www.theses.fr/2003PERP0532.
Abstract:
La phase d'installation benthique constitue une des périodes les plus critiques du cycle biologique des Sparidés. En effet, durant cette phase, les jeunes poissons de cette famille subissent une très forte mortalité par prédation qui peut décimer jusqu'à 99% des individus présents au moment de la période de colonisation des zones de nurseries. L'objectif de notre étude a été de rechercher l'influence des conditions environnementales sur la mortalité de 2 espèces de Sparidés, Diplodus vulgaris et Diplodus sargus. Nous avons également suivi l'évolution de plusieurs paramètres physiologiques et de la structure génétique de micro-cohortes de ces alevins durant toute la phase d'installation benthique. Les résultats obtenus semblent indiquer que les conditions environnementales et en particulier l'agitation du milieu ne semblent pas avoir d'influence sur les paramètres démographiques intraspécifiques (croissance et mortalité). Nous avons pu noter une évolution caractéristique de certains paramètres physiologiques (tels la disparition des individus parasités; ou l'homogénéisation de la condition nutritionnelle) qui nous permet d'envisager une sélection phénotypique directionnelle en faveur de certains individus. Du point de vue génétique il semble également que des phénomènes sélectifs se produisent, les fréquences alléliques des allèles PGM-80, 6PGD-50 et GPI-70 ayant tendance à diminuer fortement au cours de la phase d'installation benthique. Ces résultats démontrent que la phase d'installation benthique des alevins de sparidés se déroule globalement dans les mêmes conditions d'un point de vue démographique quelque soient les sites de nurseries choisis par les larves.
45
NICOLLEAU, PATRICE. "Etude structurale, ultrastructurale et analyse physico-chimique des dents des sparides et de leurs tissus de soutien." Nantes, 1990. http://www.theses.fr/1990NANT02OD.
46
au, ahesp@murdoch edu, and Sybrand Alexander Hesp. "Biology of two species of sparid on the west coast of Australia." Murdoch University, 2003. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040302.162906.
Abstract:
Various aspects of the biology of the tarwhine Rhabdosargus sarba and western yellowfin bream Acanthopagrus latus were studied. The studies on R. sarba have focused on populations in temperate coastal marine waters at ca 32oS and the lower reaches of an estuary (Swan River Estuary) located at the same latitude and in a subtropical embayment (Shark Bay) at ca 26oS, while those on A. latus were conducted on the population in the latter embayment.
A combination of a macroscopic and histological examination of the gonads demonstrated that R. sarba is typically a rudimentary hermaphrodite in Western Australian waters, i.e. the juveniles develop into either a male or female in which the ovarian and testicular zones of the gonads, respectively, are macroscopically undetectable. This contrasts with the situation in the waters off Hong Kong and South Africa, in which R. sarba is reported to be a protandrous hermaphrodite. However, it is possible that a few of the fish that are above the size at first maturity and possess, during the spawning period, ovotestes with relatively substantial amounts of both mature testicular and immature ovarian tissue, could function as males early in adult life and then change to females. Although R. sarba spawns at some time between late winter and late spring in Western Australia, spawning peaks later in the Swan River Estuary than in coastal, marine waters at the same latitude and Shark Bay, in which salinities are always close to or above that of full strength sea water, i.e. 35 ñ . While the males and females attain sexual maturity at very similar lengths in the Swan River Estuary and Shark Bay, i.e. L50s all between 170 and 177 mm, they typically reach maturity at an earlier age in the former environment, i.e. 2 vs 3 years old. Thus, length and consequently growth rate influence the timing of maturity rather than age. During the spawning period, only 9 % of the fish caught between 180 and 260 mm in nearshore, shallow marine waters had become mature, whereas 91 % of those in this length range over reefs were mature, indicating that R. sarba tends to move offshore only when it has become gphysiologically ready to mature. The L50s at first maturity indicate that the current minimum legal length in Western Australia (230 mm) is appropriate for managing this species.
Oocyte diameter frequency distributions, stages in oocyte development, duration of oocyte hydration and time of formation of post-ovulatory follicles in mature ovaries of Rhabdosargus sarba in the lower Swan River Estuary (32o 03fS, 115o 44fE) were used, in conjunction with data on tidal cycles, to elucidate specific aspects of the reproductive biology of this sparid in an estuarine environment. The results demonstrated the following. (i) Rhabdosargus sarba has indeterminate fecundity sensu Hunter et al. (1985). (ii) Oocyte hydration commences at about dusk (18:30 h) and is completed by ca 01:30-04:30 h, at which time ovulation, as revealed by the presence of hydrated oocytes in the ovarian duct and appearance of newlyformed post-ovulatory follicles, commences. (iii) The prevalence of spawning was positively correlated with tidal strength and was greatest on days when the tide changed from flood to ebb at ca 06:00 h, i.e. approximately when spawning ceases. Spawning just prior to strong ebb tides would lead to the transport of eggs out of the estuary and thus into salinities that remain at ca 35 ñ . The likelihood of eggs being transported downstream is further enhanced by R. sarba spawning in deeper waters in the estuary, where the flow is greatest. (iv) Although mature ovaries were found in R. sarba in the estuary between early July and December, the prevalence of atretic oocytes was high until September, when salinities started rising markedly from their winter minima. Batch fecundities ranged from 2,416 for a 188 mm fish to 53,707 for a 266 mm fish. The average daily prevalence of spawning amongst mature females during the spawning period of R. sarba caught in the lower estuary, i.e. July to end of October, was 36.5 %. Thus, individual female R. sarba spawned, on average, at intervals of ca 2.7 days in each spawning season. Female R. sarba with total lengths of 200, 250 and 300 mm were estimated to have a batch fecundity of 7,400, 20,100 and 54,800 eggs, respectively and annual fecundities of 332,000, 903,000 and 2,461,000 eggs, respectively.
Rhabdosargus sarba is shown to undergo size-related movements in each of the three very different environments in which it was studied. In temperate coastal waters, R. sarba settles in unvegetated nearshore areas and then moves progressively firstly to nearby seagrass beds and then to exposed unvegetated nearshore areas and finally to areas around reefs where spawning occurs. Although R. sarba spawns in the lower Swan River Estuary, relatively few of its early 0+ recruits remain in the estuary and substantial numbers of this species do not start reappearing in the estuary until they are ca 140 mm. In Shark Bay, R. sarba uses nearshore mangroves as a nursery area and later moves into areas around reefs. The maximum ages recorded for R. sarba in coastal marine waters (11 years) and Shark Bay (13 years) were far greater than in the lower Swan River Estuary (6 years). However, the maximum lengths recorded in these three environments were all ca 350 mm. Due to the production by size-related movements of differences amongst the lengths of R. sarba at given ages in different habitats in coastal marine waters, the composite suite of lengths at age was not fully representative of the population of this species as a whole in this environment. A von Bertalanffy growth curve, which was adjusted to take into account size related changes in habitat type, significantly improved the fit to the lengths at age of individuals in the composite samples for the population beyond that provided by the unadjusted von Bertalanffy growth curve. This resulted in the maximum difference between the estimates of length at age from the two growth curves, relative to the L derived from the unadjusted von Bertalanffy curve, reaching a value equivalent to 8 %. However, the maximum differences for the corresponding curves for populations in the lower Swan River Estuary and Shark Bay were far less, i.e. 1.7 and 3.2 %, respectively, and thus not considered biologically significant. Rhabdosargus sarba grew slightly faster in the lower Swan River Estuary than in either coastal marine waters or Shark Bay, possibly reflecting the greater productivity of estuarine environments.
Acanthopagrus latus is a protandrous hermaphrodite. Detailed macroscopic and histological examination of the gonads of a wide size range of fish, together with a quantification of how the prevalences of the different categories of gonad change with size and age and during the year, were used to elucidate the sequence of changes that occur in the ovotestes of A. latus during life. The scheme proposed in the present study for the protandrous changes in A. latus differed from those proposed for this species elsewhere, but was similar to that of Pollock (1985) for the congeneric Acanthopagrus australis. The ovotestes of functional males develop from gonads which, as in older juveniles, contain substantial amounts of testicular and ovarian tissue. Such ovotestes, and particularly their testicular component, regress markedly after spawning and then, during the next spawning season, either again become ovotestes in which the testicular zone predominates and contains spermatids and spermatozoa (functional males), or become ovotestes in which the ovarian zone predominates and contains vitellogenic oocytes (functional females). Once a fish has become a functional female, it remains a female throughout the rest of its life. The trends exhibited during the year by reproductive variables demonstrate that A. latus in Shark Bay typically spawns on a very limited number of occasions during a short period in August and September and has determinate fecundity. The potential annual fecundities of 24 A. latus ranged from 764,000 in a 600 g fish to 7,910,000 in a 2,050 g fish and produced a mean }1SE of 1,935,000 } 281,000. The total length at which 50 % of A. latus become identifiable as males (245 mm) is very similar to the current minimum legal length (MLL) of 250 mm, which corresponds to an age of 2.5 years less than the age at which 50 % of males become females. Current spawning potential ratios calculated over a range of alternative values for natural mortality (M) for A. latus in Shark Bay suggests that the present fishing pressure is sustainable, but that the current MLL should be reviewed if recreational fishing pressure continues to increase.
The age composition and von Bertalanffy growth parameters for Acanthopagrus latus have been determined. The relevant parameters were inserted into the empirical equations of Pauly (1980) and Ralston (1987) for estimating natural mortality (M). Total mortality (Z) was calculated using Hoenigfs (1983) equations, relative abundance analysis and a simulation based on maximum age and sample size.The two point estimates for M for A. latus, which were both 0.70 year-1, greatly exceeded all estimates for Z (range 0.18 to 0.30 year-1), which is clearly an erroneous result. To resolve this problem of inconsistent estimates, a Bayesian approach was developed, which, through combining the likelihood distributions of the various mortality estimates, produced integrated estimates for M and Z that are more consistent and precise than those produced for these two variables using the above methods individually. This approach now yielded lower values for M than Z and a measure of fishing mortality that appears to be consistent with the current status of the fishery. This approach is equally applicable to other fish species.
47
Benkirane, Ouafae. "Recherches sur l'organe de fixation des Lernaeopodidae (Copepoda Siphonostomatoida)." Montpellier 2, 1987. http://www.theses.fr/1987MON20220.
Abstract:
Une etude comparative en microscopie electronique a balayage de l'organe de fixation de 16 especes de lercaeopodidae, fixees sur des poissons, a montre qon extre)e variabilite morphologique liee a la nature du substrat. Des infestations experimentales ont permis de suivre, chez les differents stades larvaires de a. Macrotrachelus, l'apparition, la formation et l'ancrage de l'organe de fixation. Il se constitue integralement dans le chelimus iv et possede deja les composantes de celui de l'adulte. L'action spoliatrice de celui de l'adulte. L'action spoliuatrice du copepode est d'ordre trophique et mecanique par suite de la fixation
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Mouneyrac, Catherine. "Etude des caractéristiques de transport des acides aminés neutres, en relation avec la longueur de la chaîne latérale par les membranes de bordures en brosse intestinales des poissons marins : le loup (Dicentrarchus labrax) et la saupe (Boops salpa)." Lyon 1, 1993. http://www.theses.fr/1993LYO10103.
Abstract:
Le but de ce travail etait d'etudier les caracteristiques de transport des acides amines neutres differant par la longueur de leur chaine laterale (glycine, alanine, methionine, acide alpha aminoisobutyrique), par les membranes de bordures en brosse intestinales des poissons marins: le loup (dicentrarchus labrax) et la saupe (boops salpa). Pour cela, nous avons dans un premier temps etudie l'influence du calcium et du magnesium sur la purification des vesicules membranaires; puis nous avons precise les cinetiques de transport des acides amines en envisageant le role du sodium. L'emploi du calcium est prefere a celui du magnesium pour des raisons de moindre contamination d'une part, et parce qu'il ne conduit pas a une hydrolyse des phospholipides membranaires d'autre part. L'influence de la temperature sur le transport dependant du sodium de la glycine suggere qu'il n'existe pas de transition de phase dans cette bicouche pour la gamme de temperature testee. Les phospholipides des vesicules membranaires purifiees sont riches en acides gras polyinsatures. Le transport des acides amines a ete mesure par la technique de filtration rapide. En presence de potassium ont ete caracterisees deux composantes. L'une est saturable par des concentrations croissantes en substrat, particulierement pour la methionine. L'autre, de transport passif, non saturable correspondant a la simple diffusion contribue largement au transport des acides amines a longue chaine (methionine). En presence de sodium, ont ete caracterisees deux composantes a forte et faible affinite pour la glycine, alors que pour l'alanine et la methionine, il n'existe que la composante a forte affinite. Les experiences d'inhibition ont indique qu'un meme systeme participerait au transport de ces deux derniers acides amines, au moins en ce qui concerne la composante a forte affinite. La representation graphique de l'influence de differentes concentrations en sodium sur le transport des acides amines est hyperbolique avec une augmentation de la saturation surtout pour la methionine. En revanche, la constante de demi-saturation n'est pas affectee par la structure des acides amines. L'effet du sodium sur les cinetiques porte sur la vmax et/ou le kt. Il peut etre suggere une augmentation de la vitesse de translocation du transporteur. Un modele cinetique envisageant une interaction de la chaine avec le site sodium a ete propose
49
Pollard, Melissa. "Occurrence of mugilid and sparid fishes in Zostera capensis and bare sediment habitats of the Knysna Estuary." Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/54979.
Abstract:
Seagrass meadows are regarded as one of the most unique and valuable ecosystems in the biosphere, primarily because of the variety of services that they provide. Seagrass meadows serve as nursery grounds for many species and often play an important role in the juvenile stages of economically and recreationally important fish. Zostera capensis Setchell is one of the most dominant submerged macrophytes and the most common seagrass in South African estuaries and is often referred to as eelgrass. Zostera capensis meadows occupy a large area within the Knysna Estuary but little is known about their importance to associated fish assemblages. With Z. capensis meadows being under increased pressure from anthropogenic influences, it is important to establish which fish species and families utilize these habitats and what role they play in the ecology of fish assemblages within the Knysna Estuary. The primary objective of this study was to compare the use of Z. capensis and adjacent bare sediment areas by mainly large juvenile and subadult sparids and mugilids using different techniques. The two main hypotheses were as follows; 1) Mugilidae are likely to be more dominant in the unvegetated areas of the estuary littoral and Sparidae are likely to predominate within the Z. capensis bed areas of the estuary littoral. 2) The non-destructive underwater video monitoring method would yield similar fish composition data to seine netting sampling of the identical sites. Both hypotheses were assessed using data collected during this study and the analysis of historical unpublished data. Overall, Mugilidae were more abundant at bare unvegetated areas where they did most of their foraging. Sparidae were more abundant in the Z. capensis beds, which was also the habitat where they primarily foraged. With regards to the comparison of two different sampling methods, namely underwater video monitoring and seine netting, similar patterns arose with regards to the fish species observed in camera footage and those captured in the seine net, although the abundances were not always comparable.
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Marengo, Michel. "Exploitation, biologie et structure de la population du denti, Dentex dentex, en Corse (Méditerranée Nord Occidentale)." Thesis, Corte, 2015. http://www.theses.fr/2015CORT0006/document.
Abstract:
Le denté commun, plus couramment appelé denti, Dentex dentex (Linnaeus, 1758), est un poisson marin côtier (0-200m) emblématique et patrimonial en Méditerranée. Il représente un intérêt économique important pour la pêche artisanale et récréative, en Corse en particulier. En tant que prédateur supérieur, il occupe une position clé au sommet de la pyramide trophique. Il dispose un statut de conservation en étant classé comme « Vulnérable » par l’UICN. Malgré son importance écologique et économique, les données disponibles sur cette espèce sont encore limitées. L’objectif de cette thèse vise à améliorer l’état des connaissances sur l’exploitation, la biologie et la structure de population du denti en Corse. En premier lieu, un travail de synthèse bibliographique a été effectué, qui compile toutes les informations parcellaires existantes sur la biologie, l’exploitation, et la structure de population du denti sur l’ensemble de son aire de répartition. De manière générale, il existe un manque d’information, mais à travers les axes développés, ce manuscrit fourni une vision claire de l’état des connaissances actuelles sur le denti et des lacunes qu’il reste à combler. Deuxièmement, une étude a été menée pour déterminer quels facteurs pouvaient influencer les variations spatio-temporelles des captures (CPUE) du denti par la pêche artisanale et décrire la structure démographique de la population exploitée à l’échelle de la Corse. Les CPUE ont varié dans l’espace (profondeur) et dans le temps (mois), mais ont montré une stabilité annuelle. Les résultats ont montré un pic d’exploitation (des individus grands/âgés) au mois de mai pendant la période de reproduction. Cette étude a fourni également les premières cartes à fine échelle de l’exploitation au niveau spatial du denti, avec l’identification de «hot spots», qui représentent probablement des habitats essentiels dans l’histoire de vie de cette espèce. Troisièmement, une étude a comparé l’exploitation du denti par la pêche artisanale et récréative au sein de la Réserve Naturelle des Bouches de Bonifacio. Le denti est ciblé par une grande variété d’engins, ce sont la palangre (pêche artisanale) et la traine (pêche récréative) qui présentent les taux d’exploitation les plus élevés. Au niveau spatial, les captures étaient quantitativement maximales dans les zones de protection renforcée. Les résultats indiquent que la pêche récréative contribue significativement à la mortalité par la pêche de cette espèce dans la zone d’étude (3.4 t/an soit 37 % de l’ensemble des captures). Ensuite, une comparaison de trois différentes méthodes d’estimation d’âge (écailles, otolithes entiers et sectionnés) a été effectuée pour évaluer quelle structure etait la plus fiable et précise et définir les paramètres de croissance du denti en Corse. A partir des résultats obtenus, la lecture sur écaille apparait comme fiable jusqu’à cinq ans, la lecture sur otolithe entier jusqu'à 12 ans et sur otolithe sectionné peut être employée sur toutes les tranches d'âges (âge record de 36 ans). Le taux de croissance dans l’étude est relativement élevé et semble assez rapide par rapport aux études antérieures en Méditerranée. Pour finir, le dernier chapitre avait pour but d'identifier la structure du stock de denti autour de la Corse, par une approche holistique, avec une combinaison de marqueurs : les microsatellites, l'analyse de la forme des otolithes et les communautés de parasites. L’étude a mis en lumière une structuration spatiale complexe de la population, donnant de nouvelles perspectives pour la conservation des stocks de denti en Corse. Cette thèse fourni de nouvelles connaissances sur l’exploitation, la biologie et la structure de population du denti en Corse et préconise des mesures de protection pour promouvoir une gestion durable de cette importante ressource halieutique en CorseThe common dentex, Dentex dentex (Linnaeus, 1758), is an iconic marine coastal bony fish in the Mediterranean Sea. The common dentex, due to its large size, flesh quality, and high commercial value, is targeted by both artisanal and recreational fishing, especially in Corsica. As a top predator, it is a potential indicator species for the structure and functioning of the coastal ecosystems on which it depends. D. dentex is classified by the IUCN as «Vulnerable». Despite its economic and ecological importance, scientific data on this species in its natural environment are still very scant.The aim of this thesis is to improve the state of knowledge on fisheries, biology and population structure of D. dentex in Corsica. First, a review evaluates the current literature on D. dentex biology, ecology, stock structure, fisheries on its global geographical range. In general, there is a lack of information, but across the developed axes, this manuscript provided a clear view of the current state of knowledge on D. dentex and suggests future research directions to fill important gaps. Secondly, a study was conducted to determine which factors could influence the spatial and temporal variations in catches (CPUE) by artisanal fisheries and describe the demographic structure of the population exploited in Corsica. The CPUE varies over spatial (depth) and temporal scales (month), but show annual stability. The results exhibits a peak of exploitation during May (large/old specimens), probably related to reproductive strategies,. This study generated the first fine scale maps showing the spatial exploitation of common dentex and the identification of exploited fishing grounds clearly indicates the existence of ‘hot spots’, which probably represent essential habitats, of the life history of this species. Third, a study compared the exploitation of common dentex by artisanal and recreational fishing in the Bonifacio Strait Natural Reserve. It is targeted by a wide variety of gears; longline (artisanal fishing) and trolling (recreational fishing) have the highest rate of exploitation. Spatially, catches were quantitatively maximal in partially protected areas. The results suggest also that recreational fishing contributes significantly to total fishing mortality of the common dentex in the study area (3.4 t/year or 37 % of the total catch). Then, a comparison of three methods of age estimation (scales, whole and sectioned otoliths) was performed to evaluate which structure was the most reliable and accurate and define the growth parameters in Corsica. The scales appear suitable for estimating age between 0 and 5 years old, whole otoliths can be used up to 12 years and sectioned otoliths are the most accurate and reliable structure for all age ranges (age record of 36 years). The growth rate of the Corsican common dentex seems very high and quite fast compared to previous studies in the Mediterranean Sea. Finally, the aim of the last chapter was to identify the stock structure of the common dentex around Corsica Island, using a combination of markers that have different spatial and temporal scales of integration: microsatellite DNA markers, otolith shape analysis and parasites communities. A complex population structure around Corsican coasts has been reported, providing a new perspective on common dentex fishery stock conservation and management strategies.This thesis make a significant contribution to the knowledge of several aspects of the fisheries, biology and population structure of common dentex around Corsica Island and recommends protection measures to promote sustainable management of this important halieutic resource in Corsica