Letteratura scientifica selezionata sul tema "Pagrus auratus"

The ability to find a suitable settlement habitat after a pelagic larval period represents a significant challenge to marine settlement-stage larvae, and the mechanisms by which they achieve this are poorly understood. There is good evidence that olfactory cues are used by some coral reef fish larvae to locate suitable settlement habitats; however, the same understanding is lacking for marine temperate fish. Here we show for the first time that the larvae of an important commercial and recreational marine temperate fish, Pagrus auratus, can use olfactory cues to orient to appropriate settlement habitat. Using pairwise choice experiments, naive hatchery reared fish were offered water collected from a range of habitats in the Kaipara Harbour, an important nursery area for P. auratus. Larvae selected to swim towards water taken from over seagrass beds, their preferred settlement habitat, than water taken from the harbour entrance, Asian date mussel habitat, artificial seawater or artificial seawater in which seagrass had been soaked. The preference by the fish for water from the seagrass habitat over artificial seawater in which seagrass had been soaked strongly suggests that chemical cues from sources other than seagrass, such as from prey or conspecifics present in the seagrass habitat, may also be involved.

Sagitta microstructure was investigated in juvenile New Zealand snapper, Pagrus auratus, to provide a basis for daily ageing in population dynamics studies. Transverse sections produced the clearest daily increments and were the easiest to prepare. Daily increment formation was validated up to an age of 100 days by using increment counts from reared juveniles and up to about 160 days by using changes in mean increment counts from juveniles sampled from a wild population at different times. A prominent metamorphic mark was visible in transverse and frontal sections, providing a means for determining the duration of the larval period, and juvenile postmetamorphic ages. Postmetamorphic increment width varied with the age of the snapper and with season. Increment width dropped below 0.5 μm in winter and increments could not be resolved with a light microscope.

Thesis (PhD--Marine Science)--University of Auckland, 2009.
" A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Marine Science." Includes bibliographical references (leaves 161-173).

The population dynamics of juvenile snapper, Pagrus auratus, were investigated in the Hauraki Gulf, north-eastern New Zealand, between 1982 and 1990. Attention focused on age and growth, temporal and spatial variation in abundance, and recruitment. Daily increment formation was validated in the sagittae of snapper up to about 160 days old. Increment width varied with time of year, and snapper age, and increments were not resolvable with a light microscope during winter. Increment counts inside a prominent metamorphic mark showed that larval duration was 18-32 days, and was inversely related to water temperature. Spawning dates were back-calculated from increment counts in settled juveniles, and ranged from September to March with a peak in November-January. The onset of spawning was temperature dependent. Fast-growing snapper had smaller sagittae than slow-growing snapper, indicating an uncoupling of otolith and somatic growth. Snapper gonads differentiated first as ovaries during the second year of life, and then some juveniles changed sex to become males during their third year. Sex change occurred before maturity, so snapper are functionally gonochoristic. Growth was slow during the larval phase, but increased rapidly after metamorphosis to about 0.6-0.9 mm.day-1. From the first winter, growth followed a well-defined annual cycle, with little or no growth during winter, and linear growth of 0.16-0.43 mm.day-1 during spring-autumn for 0+/1+ and 1+/2+ snapper. Snapper grew faster at higher temperatures. Trawl catch rates were affected by numerous gear and environmental factors, but probably provided reasonable estimates of snapper relative abundance. Recommendations are made for improving snapper trawl survey procedures. There was a strong annual abundance cycle in the Kawau region, peaking in spring, and declining to a minimum in winter. Snapper were patchily distributed at a spatial scale of 1-2 km, probably because of preference for specific micro-habitats. Year class strength of 1+ snapper varied 17-fold over seven years, and was strongly positively correlated with autumn sea surface temperature during the 0+ year. The strengths of the 1991 and 1992 year classes are predicted to be below average, and extremely weak, respectively.

Snapper, Pagrus auratus is a valuable coastal fish species in New Zealand and forms an important commercial and recreational fishing industry in the north-east of New Zealand. Previous studies revealed evidence that this carnivorous, primarily benthic feeder consumes a non-indigenous macrobenthic species. Many non-indigenous macrobenthic species have now become established in New Zealand waters. For example, in Rangitoto Channel, Hauraki Gulf, non-indigenous macrobenthic species are prolific, with three bivalve species in particular having thriving populations: Limaria orientalis, Musculista senhousia, and Theora lubrica. The role of these species in the diet of snapper, however, is unknown. To assess the availability of indigenous and non-indigenous prey species to snapper, benthic macrofaunal assemblages throughout Rangitoto Channel were surveyed. To do so, sediment samples were collected at 84 sites. At 24 of these sites sediment was also collected for grain size analysis and at 40 of these sites the seafloor was surveyed with video. To investigate the diet of snapper, fish were collected from four monitoring sites within the channel. Bimonthly monitoring of the diet of snapper as well as the benthic macrofauna was completed at these monitoring sites and trends in the abundance of three prey species, two of which were non-indigenous species, within the sediment and the diet of snapper were compared from June to December 2008. A detailed description of the benthic macrofaunal assemblages throughout Rangitoto Channel confirmed that three non-indigenous species are established throughout this area. The analyses revealed that the diet of snapper has shifted compared to previous studies. Snapper now consume large quantities of two non-indigenous species, M. senhousia and L. orientalis. Consumption of the former species apparently results from its dominance and biomass within the sediment. It is therefore not surprising that snapper consumed large amounts of this species. In contrast, L. orientalis occurred disproportionately in the diet of snapper compared to its abundance within the sediment. I suggest that the establishment of some non-indigenous species benefits snapper.

This thesis examined the use of an estuary by the sparid Pagrus auratus, commonly known as snapper. The density and distribution of snapper (juveniles through to adults) was quantified over multiple spatial and temporal scales and associated with habitat. Juveniles enter or are spawned within the Mahurangi Harbour over the warmer months, with densities highest in March. Ontogenetic shifts in fine-scale habitat occurred. Fine-scale analysis from the beam trawl showed juvenile snapper (< 10 cm) were mostly associated with horse mussels. Larger juveniles (> 4 cm) were also associated with bare areas. The 0+ fish (from the DUV) occupied fine-scale habitat comprised of muddy to sand substrata with structure of sponges and horse mussels with and without epifauna. The remaining year-classes occupied a coarser substratum, with shell hash the major secondary structure. An artificial reef experiment showed juvenile snapper were attracted to artificial horse mussels with and without epifauna rather than bare areas or controls. The 1+ year-class increased their habitat range, occupying areas with more uniform substrata. A growth shift through to the 2+ year-class was not observed, and this may be due to increasing mortality, (natural or predation), or emigration out of the harbour. Densities of the larger year-classes decreased over the cooler months but not all snapper leave permanently, with tagging showing up to 80% of fish to be resident. Ontogenetic shifts occurred in diet with growth. Juveniles < 2 cm consumed planktonic copepods, with > 2 cm consuming benthic copepods, mysid and caridean shrimps and polychaetes. Snapper > 10 cm consumed brachyuran crabs, caridean shrimps, bivalves, polychaetes and hermit crabs, with > 30 cm fish able to consume harder shelled molluscs and bivalves. The a priori habitats were equally productive in terms of prey, and this may be advantageous for juveniles who can then select a habitat for other qualities, i.e. protection from predation. Despite the potential of snapper to utilise any sort of structure as cover or for rest, most structure within the Mahurangi are biogenic and susceptible to anthropogenic effects, especially sedimentation. The loss or decline of these biogenic species may therefore have a significant impact on the way snapper utilise the Mahurangi. Overall, understanding the ontogeny of snapper within estuaries will contribute to better management strategies for snapper in general.
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This thesis describes research designed to increase our knowledge of the nutritional requirements of Australian snapper Pagrus auratus and provide information on the potential of Australian feed ingredients to reduce the level of fishmeal in diets for this species. The apparent digestibility of organic matter (OM), crude protein (CP), crude fat (CF) and gross energy (GE) from selected animal, cereal or oilseed meals incorporated at different inclusion levels was determined. Snapper were extremely efficient at digesting the CP, CF and GE from fishmeal and rendered animal meals (range 80-100%) with the exception of meat meal, where CP and GE digestibility were lower (62-65%). The CP from oilseeds was better digested (87-91%) than OM (57%) or GE (64-67%). Digestibility of nutrients and GE from animal meals and fish oil was not influenced by inclusion level. The CP from extruded wheat was highly digestible (100-105%), but, the OM, CF and GE digestibility of extruded wheat declined as inclusion levels increased. The interactive effects of inclusion level (150, 250, 350 or 450 g kg-1) and fish size (110 vs 375 g snapper) on the apparent digestibility of OM and GE from gelatinised wheat starch were investigated. The OM and GE digestibility of gelatinised wheat starch was high (89%) at low inclusion levels, but declined significantly in both fish sizes as the level of starch increased. There was no interaction between inclusion level and size of fish and the decline in GE digestibility could be predicted by the regression; GEADC = 104.97(±3.39) - 0.109(±0.010) x inclusion level (R2=0.86). Larger fish were more capable of digesting the GE from gelatinised starch than smaller fish. Regardless of fish size, short and longer-term changes in the physiology of snapper fed or injected with carbohydrates were recorded. Liver and tissue glycogen concentrations and the hepatosomatic index (HSI) of snapper fed gelatinised starch were significantly elevated. The plasma glucose concentrations of fish injected intra-peritoneally with D-glucose increased from resting levels (0.4-4.6 mM) to 18.9 mM approximately 3 hours after injection and fish displayed a hyperglycaemic response for nearly 18 hours. In contrast, the post-prandial response to the uptake of glucose from normally digested gelatinised starch was more regulated. A dose-response study to determine the effects of digestible energy (DE) content (15, 18 or 21 MJ kg-1) on the digestible protein (DP) requirements of juvenile snapper was assessed using a four parameter mathematical model for physiological responses (4-SKM). DP content of test diets ranged from 210 to 560 g kg-1. Weight gain and protein deposition was strongly dependent on the ratio of DP:DE. According to the fitted models, diets for snapper weighing between 30-90 g and reared at temperatures ranging from 20-25ºC should contain a minimum of 28 g DP MJ DE-1 to promote optimal weight gain and protein deposition. The effect of varying the absolute content of DP and DE on the weight gain and performance of snapper (100-300 g) fed diets formulated with an optimal ratio of DP:DE was investigated. In addition, non-protein sources of DE were varied by adjusting the ratio of fish oil to gelatinised wheat starch in order to determine if different ratios of these ingredients affected performance. High-energy diets (22-23 MJ DE kg-1) suppressed feed intake, but provided DP intake was not limited by feed intake, maximum weight gain was approached. Lower-energy, lower-protien diets (15-18 MJ DE & 315-390 DP) encouraged higher feed intake but DP intake was restricted, which reduced growth potential. Snapper performed best on high-energy, high-protein diets (490 DP & 21 MJ DE), provided a significant proportion of DE was supplied as DP. Fish oil and pregelatinised wheat starch could be interchanged according to their DE values without unduly affecting fish performance in diets providing 390-490 g DP kg-1. Two utilisation studies were undertaken to investigate the performance of snapper fed diets containing increasing levels of poultry offal meal, meat meal and soybean meal. All diets were formulated with similar DP and DE contents. Snapper readily accepted feeds containing high levels of poultry meal (360 g kg-1), meat meal (345 g kg-1) or soybean meal (420 g kg-1), before weight gain and performance was negatively affected. In combination, these feed ingredients were able to replace all but 160 g fishmeal kg-1 in commercially extruded test feeds for this species. The research described in this thesis has extended knowledge of the nutritional requirements of Australian snapper by providing important information on the digestibility of Australian feed ingredients. These coefficients have been integral in formulating both experimental and semi-commercial test diets for snapper and will increase both the accuracy and flexibility of commercial diet formulations for this species. High performance feeds for snapper will contain high levels of DP, but must provide a significant proportion of DE in the form of protein. These constraints can be satisfied by using alternative, well-digested protein and energy sources that have the potential to replace all but 160 g kg-1 fishmeal.

This thesis describes research designed to increase our knowledge of the nutritional requirements of Australian snapper Pagrus auratus and provide information on the potential of Australian feed ingredients to reduce the level of fishmeal in diets for this species. The apparent digestibility of organic matter (OM), crude protein (CP), crude fat (CF) and gross energy (GE) from selected animal, cereal or oilseed meals incorporated at different inclusion levels was determined. Snapper were extremely efficient at digesting the CP, CF and GE from fishmeal and rendered animal meals (range 80-100%) with the exception of meat meal, where CP and GE digestibility were lower (62-65%). The CP from oilseeds was better digested (87-91%) than OM (57%) or GE (64-67%). Digestibility of nutrients and GE from animal meals and fish oil was not influenced by inclusion level. The CP from extruded wheat was highly digestible (100-105%), but, the OM, CF and GE digestibility of extruded wheat declined as inclusion levels increased. The interactive effects of inclusion level (150, 250, 350 or 450 g kg-1) and fish size (110 vs 375 g snapper) on the apparent digestibility of OM and GE from gelatinised wheat starch were investigated. The OM and GE digestibility of gelatinised wheat starch was high (89%) at low inclusion levels, but declined significantly in both fish sizes as the level of starch increased. There was no interaction between inclusion level and size of fish and the decline in GE digestibility could be predicted by the regression; GEADC = 104.97(±3.39) - 0.109(±0.010) x inclusion level (R2=0.86). Larger fish were more capable of digesting the GE from gelatinised starch than smaller fish. Regardless of fish size, short and longer-term changes in the physiology of snapper fed or injected with carbohydrates were recorded. Liver and tissue glycogen concentrations and the hepatosomatic index (HSI) of snapper fed gelatinised starch were significantly elevated. The plasma glucose concentrations of fish injected intra-peritoneally with D-glucose increased from resting levels (0.4-4.6 mM) to 18.9 mM approximately 3 hours after injection and fish displayed a hyperglycaemic response for nearly 18 hours. In contrast, the post-prandial response to the uptake of glucose from normally digested gelatinised starch was more regulated. A dose-response study to determine the effects of digestible energy (DE) content (15, 18 or 21 MJ kg-1) on the digestible protein (DP) requirements of juvenile snapper was assessed using a four parameter mathematical model for physiological responses (4-SKM). DP content of test diets ranged from 210 to 560 g kg-1. Weight gain and protein deposition was strongly dependent on the ratio of DP:DE. According to the fitted models, diets for snapper weighing between 30-90 g and reared at temperatures ranging from 20-25ºC should contain a minimum of 28 g DP MJ DE-1 to promote optimal weight gain and protein deposition. The effect of varying the absolute content of DP and DE on the weight gain and performance of snapper (100-300 g) fed diets formulated with an optimal ratio of DP:DE was investigated. In addition, non-protein sources of DE were varied by adjusting the ratio of fish oil to gelatinised wheat starch in order to determine if different ratios of these ingredients affected performance. High-energy diets (22-23 MJ DE kg-1) suppressed feed intake, but provided DP intake was not limited by feed intake, maximum weight gain was approached. Lower-energy, lower-protien diets (15-18 MJ DE & 315-390 DP) encouraged higher feed intake but DP intake was restricted, which reduced growth potential. Snapper performed best on high-energy, high-protein diets (490 DP & 21 MJ DE), provided a significant proportion of DE was supplied as DP. Fish oil and pregelatinised wheat starch could be interchanged according to their DE values without unduly affecting fish performance in diets providing 390-490 g DP kg-1. Two utilisation studies were undertaken to investigate the performance of snapper fed diets containing increasing levels of poultry offal meal, meat meal and soybean meal. All diets were formulated with similar DP and DE contents. Snapper readily accepted feeds containing high levels of poultry meal (360 g kg-1), meat meal (345 g kg-1) or soybean meal (420 g kg-1), before weight gain and performance was negatively affected. In combination, these feed ingredients were able to replace all but 160 g fishmeal kg-1 in commercially extruded test feeds for this species. The research described in this thesis has extended knowledge of the nutritional requirements of Australian snapper by providing important information on the digestibility of Australian feed ingredients. These coefficients have been integral in formulating both experimental and semi-commercial test diets for snapper and will increase both the accuracy and flexibility of commercial diet formulations for this species. High performance feeds for snapper will contain high levels of DP, but must provide a significant proportion of DE in the form of protein. These constraints can be satisfied by using alternative, well-digested protein and energy sources that have the potential to replace all but 160 g kg-1 fishmeal.

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.

The eggs and larvae of the New Zealand snapper Pagrus auratus are pelagic with early buoyancy provided by dilute body fluids. The swimbladder begins to develop on the third day after hatch from a dorsal evagination of the gut tube. Communication w1h the gut is lost on about the tenth day following pneumatic inflation at around day eight. At this age the gas gland system appears fully functional and capable of secreting gas. By the age of settlement at around 30 days the swimbladder is a fully functional replica of the adult form except for the lack of a resorbent capillary system which does not develop until later in juvenile life. The swimbladder of the adult is of the euphysoclist form with a dorsally located resorbent oval area and sits high in the pleural cavity. The ventral tunica externa is firmly attached to the connective tissue lining the pleural space. The adult swimbladder displaces 5.6% of the volume of the body and its volume is regulated to provide near neutral buoyancy. The connective tissue integument provides almost no restriction to volume changes brought about by vertical movements of the fish and the swimbladder obeys Boyle's Law for physiological pressure changes. The ability of the connective tissue of the tunica externa to accommodate large tissue strains is due to massive regular crimping of otherwise straight collagen fibrils allowing reversible extensions up to 130%. In all other respects however the tissue structure of the tunica externa is consistent with a tissue providing an active mechanical role. The fibrillar morphology and physicochemical properties of swimbladder collagen is consistent with the vertebrate type I form however there are interesting variations in collagen form distributed throughout the swimbladder. Fibrillar morphology of the highly extensible tunica interna is significantly different to that of the tunica externa and appears to play very little mechanical rote. The extensibilty of the tunica externa appears to be regulated by physiological stress and related to the past history of tissue strain.