Academic literature on the topic 'Gambusia holbrooki'

The introduced mosquitofish (Gambusia affinis holbrooki) is a pest species in Australia and has been implicated in the decline of populations of native fishes and anurans. However, few quantitative data exist regarding interactions between Gambusia and native aquatic fauna. We used replicated laboratory experiments to investigate predation by G. a. holbrooki on eggs, hatchlings and tadpoles of native (Limnodynastes ornatus) and non-native (Bufo marinus) anurans. Our aims were to determine (1) whether the susceptibility of anurans to predation by G. a. holbrooki changes during larval development, and (2) the potential for G. a. holbrooki as a predator of the introduced toad B. marinus. Gambusia were significant predators of all aquatic life-history stages of L. ornatus, but were significant predators of B. marinus only at the hatchling stage. When offered both species simultaneously, Gambusia consumed tadpoles of L. ornatus but avoided those of B. marinus. The differences between the responses of Gambusia to L. ornatus and B. marinus are probably due to differences in palatability and toxicity of eggs, hatchlings and tadpoles of these species. The results indicate that G. a. holbrooki is unlikely to significantly affect larval populations of B. marinus via predation. However, Gambusia has the potential to significantly affect larval populations of L. ornatus in natural water bodies where these species co-occur.

The closely related eastern mosquitofish (Gambusia holbrooki) and western mosquitofish (Gambusia affinis) have been introduced into many countries and collectively represent the most widely distributed freshwater fish in the world. We investigated genetic patterns associated with the spread of G. holbrooki in its introduced range in south-eastern Australia, by sampling 60 G. holbrooki populations (n = 1771) from major regions where G. holbrooki was initially introduced into Australia, and characterising the genetic diversity and population structure of G. holbrooki, using five polymorphic nuclear microsatellite loci and sequences from two mitochondrial genetic markers. Results were compared with published data on American and European Gambusia samples and historical records. Low microsatellite diversity and strong population genetic structuring were found within G. holbrooki in south-eastern Australia. Observed heterozygosity and allelic richness declined regionally in the order Sydney, Brisbane, Canberra, Melbourne and Adelaide. Microsatellite variation in Australia was reduced compared with native populations. Two mitochondrial DNA haplotypes of G. holbrooki were found; one was common, whereas the other was detected in one Sydney population and one Melbourne population. Cytochrome b sequence diversity was reduced compared with native and European ranges, and sequences were identical to two haplotypes previously identified. Microsatellite diversity of G. holbrooki in south-eastern Australia validates historical records of its spread, beginning north and moving south. Mitochondrial sequencing confirms that G. holbrooki is present in Australia, but the origins of Australian G. holbrooki populations remain unclear.

Clearing and staining of Gambusia holbrooki facilitated identification of juvenile fishes among the gut contents, and a feeding trial with captive Gambusia allowed assessment of gut transit time and degradation of melanotaeniid larvae. Regurgitated fishes and eggs in fixative solutions were also investigated. These techniques, extending to 12 h the post-feeding interval in which fishes may be found and differentiated among Gambusia gut contents, were tested on 631 wild-caught Gambusia collected in eastern Australia; an ingested native fish could be identified in the gut of 18 Gambusia, and a cannibalized fish in the gut of three.

Mosquitoes ( Culex pipiens L., 1758) are important vectors for diseases of both wildlife and humans. Understanding how natural factors influence mosquito abundance may provide insights into the ecology of various diseases, as well as solutions to controlling disease vectors. One of the natural factors regulating mosquito distributions and population sizes is predation. A poorly understood source of natural mosquito predation is amphibians. We determined the mosquito consumption capability of two amphibians, adult Red-spotted Newts ( Notophthalmus viridescens viridescens (Rafinesque, 1820)) and larval Mole Salamanders ( Ambystoma talpoideum (Holbrook, 1838)). We also compared mosquito consumption of eastern mosquitofish ( Gambusia holbrooki Girard, 1859), a known predator of mosquitoes, and A. talpoideum. Both salamander species were capable of consuming large numbers of mosquito larvae per day (least-square means ± 1 SE = 439 ± 20 and 316 ± 35 mosquitoes/day consumed by A. talpoideum and N. v. viridescens, respectively). In A. talpoideum, mosquito consumption scaled with body size, with the largest individual (4.4 g) ingesting 902 mosquitoes in 1 day. Gambusia holbrooki consumed 3.5× more mosquitoes during a 24 h feeding trial than similar-sized A. talpoideum. Our findings suggest that amphibians could have a substantial impact on mosquito larvae abundance, especially considering that amphibians can reach densities of up to 500 000 individuals/ha. Furthermore, we hypothesize that introduction of G. holbrooki could reduce abundances of native mosquito predators (e.g., salamanders) indirectly, through competition for invertebrate prey.

Native fish are threatened globally by invasive species, and management actions largely focus on detecting and eradicating invaders before they become established. However, once established, invaders might also be controlled by taking advantage of adaptations of threatened species to local conditions. This strategy was explored in dwarf galaxias (Galaxiella pusilla) a freshwater-dependent species of national conservation significance in Australia, threatened by invasive eastern gambusia (Gambusia holbrooki). Most habitats occupied by G. pusilla experience a seasonally variable and unpredictable hydrologic regime, where water levels substantially contract during dry periods and expand during wet periods. It was hypothesised that they are likely to have developed adaptations to surviving in these habitats by persisting without surface water. In contrast to G. holbrooki, we found that G. pusilla could withstand longer periods without surface water, including air breathing and higher respiration rates in air, than could G. holbrooki. We showed, within a single G. pusilla population, large inter-annual variability in fish densities linked to natural wetting and drying regimes. These findings indicate that periodic drying provides a way of protecting G. pusilla in water bodies where G. holbrooki has invaded, representing a strategy that takes advantage of local adaptation and metapopulation structure of G. pusilla.

The impact of the presence of the introduced poeciliid Gambusia holbrooki on the Australian pseudomugilid Pseudomugil signifer was examined in open-air tank experiments. G. holbrooki profoundly affected the breeding of P. signifer. In the presence of G. holbrooki, P. signifer did not gain weight or grow in total length, ovarian weight and fecundity were greatly reduced, and the ovaries were morphologically undeveloped. No eggs of P. signifer were observed in tanks that also housed G. holbrooki. The results indicate that, at least in a captive situation, the presence of the exotic species had a very deleterious effect on the breeding and hence possible survival of the native species. These results are discussed with reference to the conservation of Australian pseudomugilid species, especially those inhabiting confined habitats.

Defining the ecological impacts conferred by invasive fishes provides a framework for evaluating the feasibility of control efforts in invaded waterways, and for predicting the consequences of future incursions. Eastern gambusia (Gambusia holbrooki) is a remarkably successful invader of freshwater systems worldwide, with the capacity to detrimentally impact native fishes both directly (e.g. competition, predation, agonistic interactions) and indirectly (e.g. triggering trophic cascades). Here, we modelled the influence of eastern gambusia and several environmental covariates on fish species diversity, abundance and condition based on quantitative survey data collected from 93 wetlands in south-eastern Australia. We predicted that small-bodied, wetland specialist species sharing dietary- and habitat-niches with eastern gambusia would be most severely impacted, and that environmental stressors associated with wetland drying during late summer would magnify these impacts. Eastern gambusia influenced the occurrence, abundance and/or body condition of most common wetland species; however, the direction and level of impact appeared dependent on both biotic and environmental forces. From these results, we postulate that generalist life-history strategies that permit niche-segregation may release some native species from competitive/predatory pressures, allowing coexistence with eastern gambusia in resource-limited, environmentally harsh habitats, whilst specialist species that occupy narrower ecological niches may be less resistant.

Mosquitofish (Gambusia holbrooki) are native to the southeastern United States but invasive elsewhere, and are dominant predators in many ecosystems that they inhabit. Information on dispersal behavior will help better understand and predict mosquitofish metapopulation dynamics and invasions. I experimentally tested dispersal behavior of individual mosquitofish under a range of laboratory conditions relevant to field situations. Preliminary experiments showed that gender, lighting conditions, hunger and acclimation time did not significantly affect net dispersal rate. Power analysis based on this preliminary experiment determined that 6 replicate fish were sufficient for each subsequent experiment; I used 24 fish, and each fish was tested one time. Three factors that potentially could affect net swimming rate were tested: habitat of origin (permanent vs. temporary waters), water depth (3-24 mm), and the interaction between water depth and leaf litter type (upland and wetland). Fish from a temporary pond dispersed significantly faster than fish from a permanent pond, and fish dispersed significantly faster in deeper water than in shallower water. However, leaf litter significantly inhibited fish dispersal at all depths tested. Based on these experiments, G. holbrooki disperse more readily through relatively open and deeper (several centimeters) pathways between habitats such as roadside ditches, drainage canals and trails in flooded conditions. My results are useful for understanding mosquitofish dispersal behavior based on the abiotic and biotic factors examined in this experiment. I predict that mosquitofish can spread from a point of introduction at about 800 m per day, given and unobstructed path of only > 6 mm depth.
M.S.
Department of Biology
Arts and Sciences
Biology

This thesis aims to contribute to the understanding of the invasive success of two invasive fishes (Gambusia affinis and G. holbrooki). We reviewed four Internet databases and the literature to clarify their introduction history and geographical distribution, establish their introduction routes, and analyse predictors of their invasive success. A meta-analysis of the ecological impacts of mosquitofishes shows that the overall impact is: i) similar for the two species; ii) clear and strong for fish, macroinvertebrates, amphibians, and some zooplanktonic groups and more variable for taxa at lower trophic levels and for ecosystem features; iii) general for the number of aggressive acts received and decreases in density and biomass but more variable for other response variables; and iv) highly heterogeneous and context-dependent on a number of features. We estimated the mean critical swimming speed (Ucrit) of G. holbrooki as 14.11 cm s-1, which is lower than for many other fish of similar size and confirms that this species is limnophilic and its invasive success might be partially explained by hydrologic alteration. However, we demonstrate that Ucrit and maximal metabolic rate vary markedly with fish size and sex, with males having much higher values for the same weight, and thus probably being more resistant to strong water flows.
Aquesta tesi té com a objectiu contribuir a millorar la comprensió de l'èxit invasor d'aquests dos peixos (Gambusia affinis and G. holbrooki). Es van revisar quatre bases de dades d'Internet i la bibliografia per aclarir la seva història d’introducció i distribució geogràfica, establir les rutes d'introducció i analitzar els predictors del seu èxit invasor. Una meta-anàlisi de l'impactes ecològics de les gambúsies mostra principalment que l'impacte global és: i) similar per a les dues espècies; ii) clar i fort per a peixos, macroinvertebrats, amfibis, i alguns grups de zooplàncton i més variable per als tàxons de nivells tròfics més baixos i a nivell d’ecosistema; iii) general per al nombre d'agressions rebudes i la disminució de la densitat i la biomassa, però més variable per altres variables; i iv) altament heterogeni i dependent del context per una sèrie de característiques. Hem estimat la velocitat crítica de natació mitjana (Ucrit) de G. holbrooki com 14.11 cm s-1, que és inferior a la de molts altres peixos de mida similar i confirma que aquesta espècie és limnòfila i el seu èxit invasor parcialment s'explica per l'alteració hidrològica. No obstant això, vam demostrar que Ucrit i la taxa metabòlica màxima varien notablement amb la mida i el sexe dels peixos, amb valors molt més alts als mascles que a femelles del mateix pes, els quals deuen ser per tant menys vulnerables a cabals forts.

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Ciências Farmacêuticas
O interesse crescente dos estudos ecotoxicológicos nas várias classes farmacoterapêuticas tem sido o reflexo da frequente deteção destes compostos nos ecossistemas aquáticos. Esta exposição pode resultar em alterações adaptativas dos indivíduos expostos, como modificações a nível tecidular ou ativação de mecanismos antioxidantes, podendo estas ser monitorizadas de modo a determinar o impacto destes compostos nos organismos e respetivos ecossistemas. Dentro destes compostos destacam-se os antibióticos como sendo um grupo largamente utilizado na medicina humana e veterinária, resultando na sua frequente deteção nos compartimentos aquático. A tetraciclina é o antibiótico com a segunda maior taxa de deteção a nível ambiental, sendo utilizado largamente para o tratamento de patologias em humanos e animais. Na medicina veterinária, o uso dos antibióticos é ainda alargado ao tratamento profilático de infeções e promotor de crescimento. Com o interesse de determinar os potenciais efeitos ecotoxicológicos da tetraciclina em peixes, efetuou-se uma exposição aguda (96 h) de Gambusia holbrooki a concentrações crescentes deste composto (5, 50 e 500 ng/l) e pesquisou-se eventuais modificações tecidulares das brânquias e do fígado, bem como alterações da atividade das enzimas antioxidantes e a existência de danos lipoperoxidativos. O estudo da atividade enzimática permitiu averiguar quanto à presença de uma resposta de stress oxidativo (atividades das enzimas glutationa-S-transferases no fígado e nas brânquias, e a catalase no fígado), e neurotoxicidade (atividade da acetilcolinesterase no tecido nervoso). A quantificação de TBARS no músculo permitiu determinar a ocorrência de danos lipoperoxidativos. Os resultados obtidos sugerem uma relação causa-efeito entre a concentração de tetraciclina usada e as alterações histológicas nas brânquias e a atividade enzimática alterada, nomeadamente nas enzimas catalase no fígado e glutationa-S-transferases nas brânquias, sugerindo assim que este composto tem uma atividade pro-oxidante. Assim, nas brânquias as células poderão já ter entrado em stress oxidativo, o que levou a alterações histopatológicas detetáveis. No entanto, ao nível do fígado, e nas concentrações utilizadas no presente estudo, não foram observados danos histológicos significativos. The increasing number of ecotoxicological studies performed with several drugs is a natural consequence of the increasingly frequent detection of these compounds in the aquatic ecosystems. This exposure can result in adaptive changes of individuals, such as tissue alterations or activation of antioxidant mechanisms, which can be monitored to determine the impact of these compounds on the aquatic organisms and ecosystems. Antibiotics stand out as a group widely used in human and veterinary clinic, resulting in its detection in the aquatic environment. Tetracycline is the antibiotic with the second highest level of detection in the environment. It is widely used for human and veterinary treatment of infections, and as a prophylactic treatment of infections and growth promoter on animals. To determine the potential ecotoxicological effects of tetracycline on fish, Gambusia holbrooki individuals were exposed during 96 h to increasing concentrations of this compound (5, 50 and 500 ng/l) and histological alterations in gills and liver, changes in antioxidant enzyme activity and lipoperoxidative damage were recorded. The enzymatic study allowed assessing the presence of an oxidative stress response (glutathione S-transferases in the liver and gills, and catalase in the liver) and neurotoxicity (head acetylcholinesterase). The quantification of TBARS in muscle also allowed the assessment of lipoperoxidative damage. The results indicate a cause-effect relationship between the concentration of tetracycline used and the detected histological and enzymatic alterations in the liver and gills, suggesting that this compound has a pro-oxidative activity.

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Ciências Farmacêuticas
Atualmente, existem diversos grupos de agentes biocidas que podem ser utilizados em diferentes áreas, como por exemplo higiene, desinfeção, ação antiparasitária e anti-incrustantes, verificando-se assim um maior recurso à sua utilização pelo homem. Os compostos biocidas apresentam diversos usos, incorporando sobretudo tintas anti-incrustantes. O piritionato de zinco (bis (1 hidroxi -2 (1H)-piridetionato-o,s) - (T-4) zinco) classifica-se como um biocida metálico, e possui ação bactericida, algicida e fungicida. Tem sido formulado em tintas anti-incrustantes, que protegem as superfícies que se encontram expostas a um ambiente aquático, evitando assim a formação de biofilmes. Devido à sua ação biológica tem sido também utilizado para fins cosméticos, como em champôs para o tratamento da caspa e seborreia. As alterações fisiológicas em organismos aquáticos decorrentes da presença de compostos poluentes nos diversos compartimentos ambientais são hoje em dia tema de pesquisa, em face das alterações eventualmente causadas que podem ter variadas consequências deletérias ao nível dos indivíduos e dos ecossistemas. Os dados existentes recolhidos em estudos de monitorização destes compostos demonstram a presença sistemática dos mesmos em compartimentos aquáticos. No presente trabalho avaliou-se a potencial ecotoxicidade do piritionato de zinco em termos de stress oxidativo (catalase, GSTs e TBARS), neurotoxicidade (acetilcolinesterase) e danos histopatológicos no fígado e nas brânquias do peixe dulçaquícola Gambusia holbrooki, após uma exposição aguda (96 h) ao composto. O piritionato de zinco esteve na base do aparecimento de alterações histopatológicas, quer nas brânquias quer no fígado, dos organismos expostos. No entanto não se obteve nenhum resultado significativamente diferente na determinação dos índices patológicos. Relativamente aos biomarcadores testados, apenas a atividade das GSTs poderá indicar a ocorrência de efeitos pro-oxidantes, visto que para as outras enzimas utilizadas para avaliação de stress oxidativo não se obtiveram resultados significativamente diferentes do grupo controlo. At the present time, diverse biocidal agents can be used in distinct areas, such as hygiene, disinfection, antiparasitic activity, and antifouling effect, being increasingly used by humans. Biocidal compounds can be employed in a large set of applications, such as antifouling paints. Zinc pyrithione ritionato de (bis (1 hidroxi -2 (1H)-piridetionato-o,s) - (T-4) zinco) is a metallic biocide, with bactericide, algicide and fungicide activity. It has been formulated in antifouling paints, that protect surfaces exposed to the aquatic environment from the instalation of a biofilm. It has also been used in cosmetics, such as anti-dandruff shampoos. Physiological alterations in aquatic organisms exposed to pollutants in different environmental compartments have been theme of research, to diagnose deleterious effects at the individual and ecosystems levels. Already reported data show the systematic presence of these substances in the aquatic compartment. The present work intended to assess the potential ecotoxicity elicited by zinc pyrithione in terms of oxidative stress (activity of catalase, GSTs and TBARS levels), neurotoxicity (acetylcholinesteras activity), and histopathological damage in liver and gills of the freshwater fish Gambusia holbrooki, after an acute (96h) exposure to the compounds. Zinc pyrithione was capable of causing histopathological alterations, both in liver and gills of exposed organisms. However, pathological indexes were not altered. In terms of oxidative stress biomarkers, only the activity of GSTs may indicate the ocurrence of pro-oxidative effects, since the other enzymes were not responsive.

Sub-populations inhabiting the length of a stream may be subject to a number of substantially different spatial and temporal environmental influences. To be able to monitor the effects of localised disturbance throughout a catchment is of prime import, not only to the study of evolutionary processes, but also to the assessment of human intervention in catchment dynamics. To understand the ultimate effects of localised disturbance, either natural or man-maAe, on the evolution of sub-divided populations, it is essential to determine the patterns of genetic differentiation, the levels of genetic exchange between sub-populations, and the potential for natural selection or genetic drift associated with a particular habitat type or disturbance. The research outlined in this thesis, aimed at determining how disturbance over part of a species range interacts with gene flow to alter the evolutionary processes in each deme of a sub-divided population. These aims involved assessing the relative conthbütion of gene flow, natural selection and genetic drift, to the genetic structure of Mosquitofish Gambusia holbrook! populations at particular times during their yearly breeding cycle. Spatial and temporal variation in Pgi allozyme frequencies were examined relative to distance, flow velocity, and bathers to dispersal, for Gambgsia hoibrooki populations inhabiting an intennitant stream in South-eastern Queensland. Isolation by distance explained only a small amount of the genetic variation between sites. Similarly, levels of differentiation could not be explained by a simple relationship between distance and flow velocity common to both catchments examined. Barriers to dispersal allowed movement only in the downstream direction during peak flooding. Different alleles occurred in high frequencies in the headwaters of each catchment. The dominance of a single allele in headwater populations is attributed to the lack of upstream movement, and the ephemeral nature of these populations. This same allele was maintained as the most common within each catchment by downstream emigration. Inter-catchment differences were therefore attributed to the random fixation of different alleles in the headwaters of each catchment, and the dispersal of these alleles downstream during peak flood events. Significant allele frequency differences between populations in one catchment occurred despite immigration. Differentiation fluctuated over a yearly cycle, and was dependent on the level of immigration entering the lower site from alternative upstream sources. Immigration from source populations was in turn related to flow velocities in the tributaries which converged above this site. All alleles were maintained in the lower reaches of both catchments despite the input of a single allele from headwater populations. Given the mechanism by which frequency differences between sites in the lower western catchment were maintained, and severe restrictions only on upstream movement, it is hypothesised that the less common alleles are preserved in the lower reaches of each catchment, by immigration originating in tributaries where alternative alleles have drifted to relatively high frequencies. Natural selection associated with saltwater inundations and the preferential movement of Ga,nbusia size classes created and maintained genetic differences between populations in the lower western catchment, not only while these populations were isolated, but also during periods of low flow. Preferential movement also enabled selection effects to be carried into adjacent populations, causing them to differentiate from populations not receiving immigrants. Selection effects were not consistent, ocurring in some years and not others. When selection took place allele frequency differences could be maintained at the site of selection for up to a year. The influence of selection at an adjacent site receiving immigrants only maintained differences between this and other sites for a period of about one month. No selection effect could compete with gene flow during high flow velocities each year. The maintenance of genetic diversity in lower reach populations was not dependent on selection associated with habitat heterogeneity in this region of the creek, but on the input of different alleles from tributaries converging upstream. Selection would only have a significant effect on the maintenance of diversity following high flow, if it had produced allele frequency differences in the upper reaches of each catchment. The restriction of upstream movement, and the small effective population sizes associated with the ephemoral nature of headwater populations, suggests genetic drift was more important in determining the final allele frequencies, and maintaining diversity in this system.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Australian School of Environmental Studies
Science, Environment, Engineering and Technology
Full Text

The eastern mosquitofish (Gambusia holbrooki) is one of the most widely distributed and invasive inland fish. It is known that it has not been established in northern Europe or upstream of rivers, where the temperature is too low for survival and reproduction. This thesis examines how temperature affects the competitive ability and life history traits of mosquitofish. We sampled mosquitofish along latitudinal gradients and along rivers and we found that mosquitofish in more favorable environments (i.e. low latitudes and downstream river reaches) had a higher reproductive effort and lower body condition but these patterns of variation were weak and dependent on fish age. We also carried out an experiment which showed that as the temperature rises mosquitofish increases its competitive ability for resources and its aggressive behavior towards Aphanius iberus, an endangered Iberian endemism. Our results imply that climate change will favor the invasive success of mosquitofish and will increase its impact on native fish
La gambúsia (Gambusia holbrooki) és un dels peixos continentals més àmpliament distribuït i més invasors. Se sap que no s’ha pogut establir al nord d’Europa ni a trams alts de rius, on la temperatura és massa baixa per a la supervivència i la reproducció. Aquesta tesi analitza com afecta la temperatura a la capacitat competitiva i a les característiques del cicle vital de la gambúsia. Es van mostrejar gradients latitudinals i al llarg de rius i es va trobar que la gambúsia que vivia a ambients més favorables (és a dir, latituds menors i zones baixes dels rius), presentava un major esforç reproductiu i una menor condició corporal però que aquests patrons de variació eren febles i depenien de l'edat dels peixos. També es va portar a terme un experiment en què es va demostrar que a mesura que puja la temperatura la gambúsia incrementa la seva capacitat de competència pels recursos i el comportament agressiu contra el fartet (Aphanius iberus), endemisme ibèric en perill d'extinció. Els nostres resultats impliquen que el canvi climàtic afavorirà l'èxit invasor de la gambúsia i augmentarà el seu impacte en els peixos natius

Actualment una de les principals amenaces a la biodiversitat és la introducció d'espècies. Revisant 26 variables de les 69 espècies de peixos continental de la Península Ibèrica concloem que la filogènia, variabilitat i els usos de l'home són necessaris per entendre millor les diferències entres les espècies natives i invasores.
Entre les especies més afectades per la introducció de peixos es troben els ciprinodontiformes endèmics del Mediterrani. Aportem les primers dades sobre l'ús d'hàbitats ocasionalment inundats i la selecció de preses del fartet (Aphanius iberus), observant un canvi ontogenètic, clarament relacionat amb el microhàbitat.
També demostrem que la salinitat influeix en l'èxit invasor de la gamúsia, afectant la seva densitat i biologia reproductiva. Per altra banda, demostrem experimentalment que amb l'increment de salinitat la gambúsia disminueix la seva agressivitat i captura menys preses, reduint la seva eficàcia competitiva respecte dels ciprinodonts natius.
One of the main current threats to biodiversity is the introduction of invasive species. By reviewing 26 life-history and ecological variables of the 69 inland fish species of the Iberian Peninsula we conclude that phylogeny, variability and human use are needed to a better understanding of the differences between native and invasive species.
Among the most threatened species by invasive fish are the Mediterranean endemic cyprinodontiform fish. We report the first data on the use of occasionally-inundated habitats ad prey electivity by the Spanish toothcarp (Aphanius iberus). We observed an ontogenetic diet shift clearly linked to a microhabitat change.
We also demonstrate that salinity limits the invasive success of mosquitofish (Gambusia holbrooki), affecting density and life history traits. ON the ohter hand, we experimentally demonstrate that mosquitofish decreases its aggresive behavior and capture less prey, reducing its competitive efficiency with salinity increases regarding to native ciprinodonts.

La introducció d’espècies invasores, juntament amb altres pertorbacions com l’augment dels nutrients, amenacen la biodiversitat nativa globalment. Les invasions biològiques d’espècies exòtiques es troben íntimament lligades a l’activitat humana, des de l’etapa inicial d’introducció en el nou hàbitat fins a l’establiment i l’expansió. La cerca dels factors ecològics i socioeconòmics que fan que una espècie introduïda esdevingui invasora i provoqui un impacte és l’objectiu fonamental de la ciència d’invasions biològiques. Aquesta tesi s’emmarca en el context d’una invasió d’un petit peix, la gambúsia (Gambusia holbrooki) en ecosistemes subjectes a degradació ambiental a causa d’una excessiva fertilització amb nitrats. Mitjançant estudis experimentals en laboratori i en mesocosmos, però també amb estudis de camp, s’explora la hipòtesi de si l’eutrofització té una influència significativa sobre l’èxit invasor de G. holbrooki. Concretament, el primer objectiu és comprendre els mecanismes ecològics resultat de la introducció d’aquests peixos i la contaminació per nitrats i com aquests alteren la comunitat biòtica nativa i certs processos ecològics com la producció primària i la descomposició de matèria orgànica. També es vol avaluar la toxicitat directa dels nitrats sobre la salut de mascles, femelles i juvenils de G. holbrooki mitjançant l’ús de diferents biomarcadors. L’augment de la concentració de nutrients, però també la qualitat de l’habitat físic, l’abundància de depredadors i la prevalença de paràsits, podrien influir en els trets d’història de vida i l’èxit invasor de G. holbrooki. Si la seva condició física estigués influenciada per qualsevol d’aquests factors, els gestors del medi natural podrien dur a terme un control de les poblacions invasores de G. holbrooki mitjançant un enfocament que tingués en compte el conjunt de l'ecosistema, afavorint certes condicions ambientals que reduïssin el seu èxit invasor. Tanmateix, fos per eliminació directa o mitjançant aquest enfocament ecosistèmic, la reducció de l’abundància de G. holbrooki hauria de ser compensada amb la recuperació d’altres espècies natives, com ara el fartet (Aphanius iberus) i proporcionar una eficiència similar en el servei ecosistèmic del control biològic de mosquits, tant en aigües netes com eutròfiques. Els resultats indicaren una interacció insignificant entre els impactes exercits tant per la introducció del peix com per la contaminació per nitrats en l’ecosistema receptor, sent per tant els seus efectes de tipus additiu. La pèrdua de biomassa de peixos observada en concentracions altes de nitrats s'atribuiria a efectes indirectes, com ara una disminució de l'abundància de preses, i no pas per una alteració directa en la fisiologia dels peixos. Aquesta hipòtesi es confirmà en els tests de laboratori, on només els mascles i juvenils patiren alteracions lleus en l’alimentació i l’emmagatzematge de reserves. Aquesta baixa susceptibilitat de G. holbrooki als nitrats, especialment en femelles, confirma la seva alta tolerància a un ampli gradient de condicions ambientals descrita anteriorment. A més, la baixa prevalença de paràsits i l'alta variabilitat en els trets d’història de vida, aquesta última atribuïda principalment a la pròpia densitat de G. holbrooki per sobre d’altres factors ambientals, ofereix poques esperances als gestors per tal de controlar aquesta espècie invasora, a part de la completa eradicació en localitats concretes. Atesa la similar eficiència, però amb una major lentitud, de les espècies autòctones, inclús en absència de peixos, per reduir les abundàncies de mosquits en aigües eutròfiques i netes, presenta una prova evident que la introducció de G. holbrooki representa una amenaça innecessària per al servei ecosistèmic natural. La superioritat competitiva de G. holbrooki sobre les espècies natives, juntament amb la dificultat d’eradicar-la una vegada establerta, fa que siguin prioritaris la prevenció de noves introduccions de G. holbrooki per al control biològic de mosquits, però també la restauració de les poblacions de competidors natius.
Invasive species, together with other perturbations like nutrient enrichment, threaten native biodiversity worldwide. This thesis is framed within the context of the invasion of a small fish, the eastern mosquitofish Gambusia holbrooki (Girard, 1859) in ecosystems subject to environmental degradation due to excessive fertilisation with nitrates. By means of experimental and field observational studies, the hypothesis of whether eutrophication mediates the invasive success of G. holbrooki is explored. Specifically, the initial aim is to understand the ecological mechanisms exerted by fish introduction and nitrate pollution in altering the native communities, the ecological processes and their interaction. Nutrient enrichment causing eutrophication, but also physical habitat quality, abundance of predators and parasites prevalence could influence the life history and the invasive success of G. holbrooki. Should the invader fitness be mediated by any factor, managers could carry out an ecosystem approach by favouring such desired conditions against the invader success. Either by direct elimination or through an ecosystemic approach, the loss of G. holbrooki populations should be substituted by other native species, such as Aphanius iberus and provide a similar mosquito control efficiency in clean and eutrophic waters. Results indicate a negligible interaction between the impacts exerted by both fish introduction and nitrate pollution on the recipient ecosystem. The loss of fish biomass in high nitrate concentration would be attributed to indirect effects such as a decline in prey abundance, rather than a direct alteration on fish physiology. This low susceptibility of G. holbrooki to nitrates, especially in females, confirms its high tolerance to a wide gradient of environmental conditions reported by previous authors. Moreover, the low prevalence of parasites and the high variability of life history traits, mainly attributed to G. holbrooki density in the pond over other environmental factors leave managers with low chances of controlling the invader apart from its eradication. Given the similar but slower efficiency of the native community both in eutrophic and clean waters in reducing mosquito abundances and the difficulty of eradicating G. holbrooki once established, favouring the presence of native competitors and preventing further introductions of G. holbrooki for biological control seems a priority.

Monografia apresentada à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de licenciada em Ciências Farmacêuticas.
A presença de compostos com capacidade neuroactiva nos ambientes aquáticos tem sido uma das principais preocupações dos ecotoxicologistas que avaliam os potenciais efeitos de fármacos nos organismos aquáticos. As alterações fisiológicas decorrentes da presença de resíduos de medicamentos de utilização humana nos diversos compartimentos ambientais são hoje em dia tema de pesquisa, em face das alterações eventualmente causadas nos organismos não alvo. Os dados existentes actualmente, recolhidos em estudos de monitorização destes agentes em compartimentos aquáticos e que visam avaliar o seu impacto, demonstram a presença sistemática de compostos deste tipo nas mais variadas matrizes; no entanto, existe uma manifesta falta de dados científicos que demonstrem, ou não, que estes compostos podem ser potencialmente nocivos do ponto de vista ambiental. O composto sobre o qual incidiu o presente estudo, o diazepam, é um composto de utilização como anticonvulsivante, tranquilizante e relaxante muscular, e existem já evidências que decorrem de estudos já publicados, de que pode estar envolvido em cenários de stress oxidativo. Sendo um composto que actua sobre uma via de comunicação fisiológica altamente conservada (inibição da neurotransmissão por aumento da condutância ao cloreto ao nível das células neuronais), este composto pode potencialmente comprometer um vasto leque de funções neuronais em muitas espécies. Assim, e visto actuar directamente ao nível do sistema nervoso central dos organismos, foi o nosso objectivo estudar alterações enzimáticas e histológicas na espécie Gambusia holbrooki, após exposições agudas (96 horas) a diversas concentrações deste agente (0,0025; 0,005; 0,02; 0,02; 0,04μg/l). Os efeitos decorrentes da exposição ao referido composto foram avaliados ao nível da actividade enzimática (catalase e glutationa S-transferases) e de alterações histológicas observadas no fígado e brânquias dos organismos expostos. O diazepam causou evidentemente alterações regressivas histológicas nas brânquias e no fígado dos animais expostos às três concentrações mais altas. A actividade da catalase mostrou também estar aumentada, indicando stress oxidativo. Já o caso da glutationa S-transferase demonstrou não ser um biomarcador viável para a avaliação do risco ambiental, pelo menos em exposições agudas.

<i>Abstract.</i>—We document a simple electrofishing-only monitoring program for assessing fish assemblages across large spatial extents. First, we demonstrate the justification for using only electrofishing for the monitoring. Second, we demonstrate the usefulness of having a well-designed surveillance-monitoring program in place to demonstrate the effect of landscape disturbances. Implementing electrofishing alone means that multiple sites can be sampled in a single day and there is no need to return to clear nets or traps within a sampling site. Whereas electrofishing alone does not return full species lists within sampled sites, we demonstrate that when data are aggregated up to the watershed or catchment extent, more than 90% of species are included. Analyses that do not require a census of species, such as bioassessment of river health can be readily carried out using electrofishing data. The Murray–Darling basin, Australia, was sampled with the recommended large-extent electrofishing program between 2004 and 2012, a period that saw the region subjected to large-scale variations in river flow levels spatially and temporally. We fit generalized additive models to the electrofishing data in conjunction with river flow data to document large-extent relationships between fish species occurrence and relative flow levels for the previous 3 d, 3 months, or 3 years. We found that several small-bodied species, Eastern Mosquitofish <i>Gambusia holbrooki</i>, Flathead Gudgeon <i>Philypnodon grandiceps</i>, and Australian Smelt <i>Retropinna semoni</i>, were more likely to be collected when conditions were drier in the past 3 d to 3 months, whereas common medium and large-bodied species were less likely to be collected when flow was lower over the previous 3 months to 3 years.