<p>The need to protect size and age structures from selective harvest in order to maintain sustainable fish stocks has been emphasized in recent literature. The Big Old Fat Fecund Female Fish (BOFFFF) hypothesis has been influential in discussions of changing stock management strategies, and postulates that larger, older females have a disproportionate input into stock recruitment due to physiological advantages. In this study, we utilize a meta-analysis approach to test the assumption of the BOFFFF hypothesis, that larger female fish produce larger eggs and more viable offspring, at a broad scale. Following the meta-analyses, we assess whether larger females from a subset of studies use their gonadal investment more efficiently than small females. From our meta-analyses, we found positive, significant intraspecific relationships between female size and egg size. Moreover, we found positive associations between egg size and offspring viability (offspring size and survival). However, we found in a subset of studies that although proportional survival of offspring often increases with egg size, females that produced larger eggs yielded fewer surviving offspring per unit gonadal investment. This reduced efficiency in reproductive investment is a product of the trade-off between egg size and fecundity. We conclude that although larger females may appear to produce more viable individual offspring, their input to stock recruitment, according to total stock gonadal biomass, may not be disproportionate, as stated by the BOFFFF hypothesis. However, we did not account for whether the benefits of maternal effects extend beyond the larval stage.</p><p>The theory of optimal egg size implies that fish trade off between fecundity and individual gonad investment according to their environment. Past interspecific studies suggest that in general, fishes in large, marine systems produce smaller eggs than those in small, freshwater systems. This study aims to compare egg size intraspecifically among small and large systems. In particular, we focus on populations from the Laurentian Great Lakes, which exhibit similar broadscale physical processes as marine systems, and smaller inland lakes (<1,000 ha), whose ecosystems contain many of the same species. In 2018 and 2019, we collected egg samples from spawning walleye (<i>Sander vitreus</i>) and yellow perch (<i>Perca flavescens</i>) in both inland lake and Great Lake populations. From each female, we recorded total lengths, and measured average diameters of ten eggs. Using ANCOVA models, we compared mean length-adjusted egg diameters intraspecifically among populations of both species. For both walleye and yellow perch, we found that females from inland lakes produced larger mean length-adjusted egg diameters than those of the Great Lakes. This pattern was particularly evident for yellow perch, whereas for walleye the pattern was relatively weak, potentially due to stocking eroding population-specific selection for egg size. These intraspecific patterns are consistent with cross-system interspecific variation in fish egg size.</p>

M.Sc. (Zoology) / Concern has been shown by Ezemvelo KZN Wildlife for the state of the Lower Pongolo River and Floodplain due to the ever increasing urban and industrial development in the area. This increase in development poses a threat to the fish populations within the system and their ability to support the surrounding communities. Continued spraying of pesticides e.g. DDT within the area are adding to stresses placed on the fish populations through decreasing water quality. The effectiveness of environmental water flows suggested by White et al. (1984), have never been assessed by conservation authorities. This means that the authorities have been unable to fulfil their legislative obligations to establish management and conservation plans (Hughes et al., 2001). Work on the biological responses of fish to anthropogenic stressors such as organic pollutants and metals; have been conducted by a group of experts in the field of ecological health. This section of the project focusses on two fish species, Hydrocynus vittatus and Synodontis zambezensis, sampled within the study area and used for biomarkers and tissue chemical level determination. Standard techniques were applied for Organochlorine Pesticide (OCP) analysis according to Yohannes et al. (2013) and these results have been compared to biomarker responses which have also been completed following standard protocols. Results found within both fish species, show the relationship between accumulation of toxicants and biomarker responses. The highest levels of ΣOCPs where found within H. vittatus at (Mean ± SE) 1101.61 ± 610.97 ng/g lipid weight, the highest constituent being technical grade Dichlorodiphenyltrichloroethane (DDT). High levels of ΣDDT were also found in S. zambezensis, but were lower than levels in H. vittatus and these levels correspond with positioning of each species within the food web. H. vittatus occupies a much higher level in the food web as they are top predators and S. zambezensis falls lower down on the food web due to their reliance on detritus and only small invertebrate species for food. Biomarker responses are clearly affected by bioaccumulation levels and this is especially evident within H. vittatus as Achetylcholinesterase (AChE) is greatly inhibited by high levels of ΣDDT. Changes in the level of biomarker responses are not as apparent in S. zambezensis and this is believed to be food web linked, due to differences in bioconcentration. Data collected during this study will contribute to baseline data on S. zambezensis and add to already accumulated data on H. vittatus. This new data will also help with the improvement of or alteration to already present monitoring programmes in the study area.

Water temperatures are a fundamental water quality component, and a key abiotic determinant of fish distribution patterns in rivers. A river 's thermal regime is the product of a multitude of thermal drivers and buffers interacting at different temporal and spatial scales, including, inter alia, air temperatures, flow volumes (including groundwater flows and lateral inputs from tributaries), channel geomorphology and riparian vegetation. "Healthy" river systems are self-sustaining, with adequate thermal variability to maintain biotic diversity. Temporal variability of flow volumes and water temperatures, and how these change along the longitudinal axis of a river, contribute towards a rivers "signature". Rivers that have had their signatures altered through anthropogenic impacts may no longer be sustainable, and require varying levels of management. Successful river management should include a quantification of these signatures , a definition of the "desired" state which management aims to achieve, associated "thresholds" of change or concern, and monitoring programmes. Such an approach requires flexibility and adaptability, as well as appropriate tools being available to natural resource managers. Indices, the utility of which are enhanced when included in predicative modelling systems, are a common means of assessing system variability and change. The degree of confidence placed in such tools depends on the level of fundamental science, and the degree of system understanding, underpinning them. This research contributes to the understanding of the ecological significance . of water temperatures in variable semi-arid river systems, using the Sabie River (Mpumalanga, South Africa) as a case study, and indices derived from biological indicators (Chiloglanis , Pisces: Mochokidae) to quantify the effects of cumulative changes in heat units against a hypothesised critical water temperature threshold. Hourly water temperatures for 20002002 collected at nine sites in the main rivers of the Sabie catchment, together with biannual surveys of relative abundances and community patterns of fish collected using standard electrofishing techniques, were used to provide the basis for a modelling system which aims to provide river managers with a tool for quantifying changes to the thermal regime of the Sabie River. This modelling system consisted of a suite of pragmatic models, including multiple linear regression models for simulating daily maximum water temperatures, and simple cause-and-effect relationships between biological indices (change In condition factor and change in the ratio of relative abundances of two species of Chiloglanis) and annual metrics of time-of-exposure to heat stress. It was concluded that changes in the thermal regimes of the rivers in the Sabie catchment are likely to lead to changes in fish distribution patterns, and a decline in river health. Inherent system variability suggests that management decisions will be made in the face considerable uncertainty. Indirect management of water temperatures may be possible through maintenance of flow volumes and flow variability. However, the most appropriate management approach for maintaining fish diversity within these rivers is to ensure that obstacles to fish migration are minimized, to maximise the ability of river biota to respond to thermal changes, by accessing suitable alternative habitats or refugia. Future research should focus on extending the time series of water temperatures from such river systems, and further understanding the drivers and buffers contributing to the thermal regimes of variable semi-arid river systems in South Africa. Additional testing of the validity of the hypothesized relationships between abiotic processes underpinning biotic patterns should be undertaken. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2003.

The freshwater fish fauna of southern Australia is characterised by low species richness and high endemism in groups displaying southern temperate, temperate-subtropical or temperate-tropical distributions. Comparatively few studies in Australia have incorporated modern molecular techniques to delineate species boundaries and define within-species conservation units. This is problematic because freshwater fishes are likely to show high levels of cryptic speciation and marked spatial sub-structure, and is information which is needed to conserve biological diversity and maintain the integrity of ecological communities and processes. The current study uses a ‘combined evidence’ approach, led principally by a set of nuclear genetic markers (allozymes), to assess species boundaries, spatial sub-structure and conservation units in obligate freshwater fishes from southern Australia. A literature review (Chapter 2) concerns the nature and effects of fragmentation in freshwater environments. It considers the implications for freshwater fishes and the types of extrinsic and intrinsic characteristics, both natural and human accelerated, that might drive population fragmentation and divergence. This theoretical framework is then applied to a suite of six largely co-occurring species groups with contrasting biological characteristics, and derive hypotheses about expected levels of genetic divergence across and within different drainages. Major findings Species of Retropinna (Chapter 3) are widespread and generally regarded as ‘common’ and mobile. Allozyme analyses revealed species-level and population-level sub-divisions, including five distinct species with contiguous ranges and no evidence of genetic exchange. Three occur along the eastern seaboard (including three instances of sympatry), another in coastal and inland southeastern Australia and Tasmania, and a fifth in the Lake Eyre Basin. There is no indication of a simple ‘tasmanica’ versus ‘semoni’ dichotomy, but instead a complex pattern involving discrete clusters for the Upper Murray plus Darling rivers, Lower Murray, Glenelg River and Tasmanian regions. These findings have implications for biodiversity, conservation and ecology. This chapter has been published in modified form (Marine and Freshwater Research 58, 327- 341). Nannoperca obscura (Chapter 4) is a small demersal fish with specialised habitat requirements. It is under threat of extinction, particularly in the western section of its range. Combined nuclear and matrilineal genetic data identified congruent within-species sub-structure, divided by patternsof distribution and biogeography. Four monophyletic mtDNA lineages, each distinct at multiple nuclear loci, indicate four Evolutionarily Significant Units (ESUs), namely (1) Lake Alexandrina in the Murray-Darling Basin (MDB), (2) Glenelg River, Millicent Coast River Basin and the outlying Mt Emu Creek, (3) Merri River and associated coastal streams, and (4) the eastern range section. Additional genetic and ecological data support multiple Management Units (MUs) within ESUs for individual or groups of river basins separated by marine barriers. Nannoperca australis (Chapter 5) has a similar character to its aforementioned congener, except that it occurs across a much wider area. Although generally common, particular populations are threatened, especially in the MDB. Allozyme analyses of 57 populations confirm the presence of two divergent species, with an eastern species containing two ESUs: (1) Gippsland and Flinders Island, and (2) Ansons River in northeastern Tasmania. The western species shows sub-structure across its range, including a separation of MDB and coastal populations as two heterogenous ESUs. The Lower Murray region (Mount Lofty Range streams and the Lower Lakes) harbours a remarkable level of between- and within-population diversity, underscoring its importance for conserving evolutionary potential. Mogurnda adspersa (Chapter 6) has been presumed extinct in South Australia since the early 1970s and has also been assumed lost from the southern MDB. This chapter reports on the rediscovery of M. adspersa from a wetland near the terminus of the Lower Murray, some 2500 river kilometres from the nearest known population. The nature and basic ecology of this population is documented, but the combined effects of drought and water abstraction recently have led to the probable extirpation of the wild population. A combined allozyme and mtDNA dataset confirmed the ‘nativeness’ of the population as a distinct sub-population (and MU), with a moderate level of allele heterogeneity. This information provides a platform for captive breeding as a conservation measure. The endemic genus Philypnodon (Chapter 7) contains two nominal species: P. grandiceps and the long recognised but only recently described P. macrostomus. The former is considered widespread and common (near ubiquitous), whereas the latter is more patchily distributed. Some tolerance to marine conditions is indicated, suggesting that there may be less sub-structure, but allozyme analyses of 269 individuals indicate the presence of multiple, species-level taxa within both described species. This obscures interpretations of existing ecological data. Although the presence of genetically-similar populations within and across some drainage divides indicates higher levels of gene flow, the pattern is complex and suggests historic genetic exchange between some but not other geographically-adjacent taxa. The freshwater blackfish genus Gadopsis (Chapter 8) has been a problem group for taxonomists, and it is unclear where the group is placed phylogenetically and how many species occur. Northern and southern forms on respective sides of the Great Dividing Range have been proposed, but with limited supporting evidence. Its dispersal ability (hence predicted genetic structure) is obscured by opposing life-history traits, including large body size (i.e. good swimming ability) versus habitat specialisation, demersal larvae and restricted home ranges. This chapter provides a genetic overview incorporating 61 locations across the range, and demonstrates unequivocally the presence of distinct northern and southern species of G. ‘marmoratus’. Moreover, distinct genetic discontinuities involving geographically abutting lineages indicate the likely presence of multiple ESUs within each species. A comparison of the allozyme data with previous mtDNA studies also identified two ESUs within G. bispinosus. Overall, considerable complexity is demonstrated signalling the need for a review of how the southern Australian fish fauna should be viewed, studied and protected. The genetic data also provide insight into the interplay of intrinsic biological characters (e.g. dispersal ability, population ecology) with historic and contemporary extrinsic environmental factors (e.g. fragmentation, biogeographic processes). Comparisons between and within traditionally-defined species are problematic, however, owing to multiple species-level splits and other genetic divisions that may have matching biological counterparts. Together with other reports in the literature, the findings presented herein have significant conservation implications, particularly given the rapid pace of human-mediated change in some regions that house high species and genetic diversity and unique evolutionary components, notably southeastern Queensland (especially the Mary River) and the lower River Murray in South Australia. Other regions displaying high genetic substructure or divergent populations include the Clarence River and Lachlan River in New South Wales; Gippsland, Goulburn River, Glenelg River and Mt Emu Creek in Victoria, and the Macquarie River and Ansons River in Tasmania. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1339749 / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2008

Ph.D. / The Crocodile River catchment, in Mpumalanga, is one the most intensively used catchments in South Africa. The large number of intensively cultivated crops grown in the middle and lower subcatchments; industrial discharges; highly intensive irrigation; and extensive areas of exotic afforestation in the upper and middle sub-catchments has dramatically changed land use patterns within the catchment. The Middle Crocodile River sub-catchment is also impacted by intensive urbanisation; around Nelspruit, KaNyamazane and Matsulu. The Kaap River sub-catchment has been intensively mined for minerals and the impacts of these mining operations are still reflected in the water quality of streams and rivers in this sub-catchment. The downstream uses of the Crocodile River's water quality are the aquatic ecosystem, the Kruger National Park (as the river is the southern boundary of the park) and Mozambique (international obligations). The Crocodile River catchment supports one of the richest fish species diversities in South Africa. It is therefore important to determine the impacts of these land use activities on the fish populations and the potential human health risks if fish are consumed. In the present study data from five gauging stations for each of the main tributaries draining the five sub-catchments (the Upper, Middle and Lower Crocodile River, Kaap and Elands Rivers) were used. The water quality and quantity was determined from Department of Water Affairs and Forestry's (DWAF) National Hydrological Chemical Data Bank. Assessments of water quality (chemical, physical), sediment characteristics, and fish biological characteristics were undertaken at each of the chosen sampling sites. Water and fish samples were collected seasonally on ten sampling trips during the study period, June 1989 to September 1992. Eleven species of fish were collected, by means of gill and seine nets, at eight sites. The biological characteristics of the larger fish captured were measured and tissue (gills, liver, muscle, intestine, ovaries, testes and abdominal fat) samples were collected. These samples were analysed for eleven metals and Pyrethroid, Carbamate, Organochlorine, Organophosphate and Triazine pesticides. Sediment core samples were collected and determinations made of particle size, percentage organics, metals and pesticides. Standard methods were used for the determination of .the metal and pesticide concentrations in the water, sediment and fish tissues. The pesticide use per crop for South Africa was determined from a data-base. This data was used to determine the potential pesticide runoff from the different crops in the sub-catchments and to compare with the sediment and fish tissue levels recorded. The water quality status of the Crocodile River catchment is impacted by a variety of diffuse and point sources of pollution. The water quality indicated that diffuse sources of pollution originated from afforestation in the Upper, Middle and Kaap River sub-catchments; current and abandoned mining activities in the Kaap River sub-catchment; runoff from irrigated lands in the Middle, Lower and Kaap River sub-catchments; and wastes from industrial activities in the Elands and Middle sub-catchments. Point sources of pollution in the Crocodile River include ndustrial and waste water treatment works discharges mainly in the Middle sub-catchment.

M.Sc. (Zoology) / The Vaal River system is constantly subjected to pollution from various industrial, mining and agricultural activities. Consequently, pressure is continually exerted on the health of its fish communities and it was suspected that this may be a contributing factor to the repeated fish kills that have occurred in various sections of the river over the past few years. The aim of this study was to assess the health status of three fish species that were affected by the most recent mass fish mortality in the Vaal River. This was done using a combination of techniques including a histology-based health assessment (HHA) that involved a standard fish necropsy, the evaluation of blood parameters as well as a microscopic assessment of the liver, kidney, gills, and gonads. The histological results were semi-quantitatively assessed. Selected chemical substances were also tested for in water, sediment and the skeletal muscle tissue of the fish. Clarias gariepinus, Labeo capensis and Labeo umbratus specimens were collected from the Vaal River, approximately 2480m below the Vaal Dam (Latitude 26°51'17.47"S; Longitude 28° 7'16.58"E) following the latest occurrence of a fish kill in November 2011. Fish were collected using gill nets. Water was sampled in triplicate at three locations, and in situ measurements were done for selected physico-chemical parameters. Sediment samples were also collected and subjected to a sequential extraction technique and quantification of the heavy metals was done using Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Metals in skeletal muscle tissue and water were quantified using the same technique. An analysis of variance (ANOVA), followed by the appropriate post-hoc test was performed to determine differences between means of variables i.e. morphometric, histological, substance concentration and blood parameters...

Orientador: José Augusto Senhorini / Resumo: O Rio Santa Bárbara, pequeno afluente do Rio Sapucaí-Mirim, drena uma área de 1.013 km². Está inserido na bacia do alto rio Paraná, região considerada uma província ictiofaunística natural. Este trabalho estabeleceu como objetivo principal registrar a ictiofauna desse rio, de algumas de suas lagoas marginais e de seu afluente Rio Potreiro, bem como caracterizar o grau de antropização de sua bacia. Quatro campanhas foram realizadas, duas na estação seca e duas na estação chuvosa. Um total de 922 exemplares foram coletados, considerando os doze pontos de amostragens selecionados (seis pontos em lagoas e seis pontos em rios), distribuídos em 33 espécies representativas de 16 famílias e 6 ordens. A ordem Characiformes revelou-se a mais representativa (63%), seguida das ordens Perciformes (13%) e Siluriformes (12%). Com relação às famílias, Characidae (41%) foi a mais abundante, seguida pelas famílias Cichlidae (13%) e Poeciliidae (11%). Um espécime de Brycon nattereri foi coletado no Rio Santa Bárbara, espécie criticamente ameaçada no estado de São Paulo; duas espécies não nativas foram encontradas (Metynnis maculatus e Oreochromis niloticus), representado 0,7% do total de espécimes coletados e três espécies tiveram o seu primeiro registro para a bacia do Rio Sapucaí Mirim: Hyphessobrycon bifasciatus, Moenkhausia intermedia e Brycon nattereri. Foram identificadas 65 lagoas marginais ao longo da bacia do Rio Santa Bárbara (45 permanentes, 19 temporárias e 3 meandros abandonados), ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Santa Bárbara River, a small tributary of the Sapucaí-Mirim River, drains an area of 1,013 km². It is inserted in the upper Paraná river basin, a region considered a natural ichthyofaunistic province. This work aims to record the ichthyofauna of this river, some of its marginal lakes and its affluent Rio Potreiro, as well as to characterize the degree of anthropization of its basin. Four campaigns were carried out, two in the dry season and two in the rainy season. A total of 922 specimens were collected, considering the twelve sampling spots selected (six spots in lakes and six spots in rivers), distributed in 33 representative species of 16 families and 6 orders. The Characiformes order came out to be the most representative (63%), followed by Perciformes (13%) and Siluriformes (12%). Regarding the families, Characidae (41%) was the most abundant, followed by families Cichlidae (13%) and Poeciliidae (11%). A species of Brycon nattereri was collected in Santa Bárbara River, a species critically endangered in the state of São Paulo, two non-native species that were found (Metynnis maculatus and Oreochromis niloticus), represented 0.7% of the total specimens collected and three species had the first record for the Rio Sapucaí Mirim basin: Hyphessobrycon bifasciatus, Moenkhausia intermedia and Brycon nattereri. A total of 65 marginal lakes were identified along Santa Bárbara river’s basin (45 permanent, 19 temporary and 3 abandoned meanders), mapping the spatial patterns of the... (Complete abstract click electronic access below) / Mestre

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Submitted by Sandra Pereira (srpereira@ufrrj.br) on 2016-08-05T12:49:34Z No. of bitstreams: 1 2010 - Sonia Maria Cursino dos Santos.pdf: 1464196 bytes, checksum: c7ebc61346b0236e31bd681219da0196 (MD5) / Made available in DSpace on 2016-08-05T12:49:34Z (GMT). No. of bitstreams: 1 2010 - Sonia Maria Cursino dos Santos.pdf: 1464196 bytes, checksum: c7ebc61346b0236e31bd681219da0196 (MD5) Previous issue date: 2010-10-06 / The Pantanal provides great biotic diversity, having different characteristics in times of flood and drought, hosting around 263 species of fish. The studies of the ecological host-parasite relationship in fishes of the Cuiab? River, North Pantanal (MT) are scarce. This study aimed to study quantitatively and qualitatively the endoparasite communities of migratory fish of commercial importance of this location, check the fluctuation patterns of these indices and their relation to the total length and the sex of host, and the cluster analysis of the similarity between the components communities of endoparasites from different hosts. The samples were taken during the years 2005 to 2009 on the River Cuiab? - Pantanal National Park (PARNA-Pantanal) at 17 ? 50 '48 "S 57 ? 24' 6" W in the state of Mato Grosso, Brazil, 376 specimens: Pseudoplatystoma corruscans - 50, P. fasciatum - 50, Piaractus mesopotamicus - 85, Prochilodus lineatus - 72; Zungaro zungaro-50 and Salminus brasiliensis - 87. Twenty-three species of endoparasites were identified: five digenean, eight cestodes, seven nematodes, two acanthocephalan and one pentastomid. We collected 10,418 specimens of endoparasites, of wich 6162 (59.15%) were collected from P. mesopotamicus, 1249 (11.99%) of P. fasciatum, 1173 (11.26%) of Z. zungaro, 1167 (11.2%) of P. corruscans. The pattern of aggregate distribution of parasites was observed for all species. The fishes from the family Pimelodidae analyzed showed the greatest diversity of species, although without the presence of any dominant species of endoparasites. The relationship of body length between the host parasite prevalence were positive for the parasitism of P. lineatus by N. (N.) curemai and by A. compactum, and of P. corruscans by S. oxycephala. On the other hand, parasitism of P. corruscans by Porrocaecum sp. showed a negative relationship between abundance and host growth. In Z. zungaro only the abundance of P. rugosa and Porrocaecum sp. showed positive relationship with the length of the fish. The sex of the host had influenced significantly the abundance of N. (N) curemai in P. lineatus, of S. spectatus in P. mesopotamicus and the prevalence of S. oxycephala in P. fasciatum, suggesting the existence of ecological and behavioral differences between male and female hosts. Cluster analysis of similarity between the compositions of endoparasites of migratory fish has resulted in two main groups well differentiated, with only 16.03% similarity between them. The first group was formed by piscivorous fish and the second by omnivores and detritivores. Among pimelodids the composition of their communities have 50% of similarity reaching to 87.5% of similarity between P. corruscans and P. fasciatum. The S. brasiliensis (Characidae) showed qualitative similarity of 39.68% compared to the internal group comprised of Pimelodidae. The other main group was composed by the omnivorous P. mesopotamicus (Characidae) and the detritivore P. lienatus (Prochilodontidae). Prochilodus lineatus showed 22.22% of similarity in the composition among their endoparasites. As the quantitative similarity, only a core group was formed. The similarity between the pimelodids was 50.35%, reaching to 67.29% between P. faciatum and P. corruscans. Salminus brasiliensis shared 30.46% of similarity between the quantitative pimelodids and 12.41% between P. mesopotamicus which, in turn, showed only 2.02% of quantitative similarity with P. lineatus. Among the migratory fish of commercial interest in Northern Pantanal of Mato Grosso, the similarity on the composition and structure of their endoparasite communities was strongly influenced by the phylogenetic relatedness hosts, as well as by the piscivorous feeding habits, coupled with the distribution of the fishes at the water?s column / O bioma Pantanal apresenta uma enorme diversidade bi?tica, possuindo diferentes caracter?sticas nas ?pocas de cheia e seca, albergando cerca de 263 esp?cies de peixes. Escassos s?o os estudos da rela??o ecol?gica parasito-hospedeiro em peixes do rio Cuiab?, ?rea do Pantanal Norte (MT). Este estudo teve como objetivos estudar quantitativamente e qualitativamente as comunidades de endoparasitos de peixes migradores de import?ncia comercial desta localidade, verificar os padr?es de flutua??o destes ?ndices e sua rela??o com o comprimento total e o sexo dos hospedeiros e analisar o agrupamento dos ?ndices de similaridade entre as comunidades componentes de endoparasitos em diferentes hospedeiros. Foram coletados durante os anos de 2005 a 2009 no rio Cuiab? ? Parque Nacional do Pantanal (PARNA-Pantanal) a 17? 50? 48? S e 57? 24? 6? W do estado de Mato Grosso, Brasil, 376 esp?cimes: Pseudoplatystoma corruscans ? 50, P. fasciatum ? 50, Piaractus mesopotamicus ? 85, Prochilodus lineatus ?72; Zungaro zungaro? 50 e Salminus brasiliensis ? 87. Vinte e tr?s esp?cies de endoparasitos foram identificadas: cinco digen?ticos, oito cest?ides, sete nemat?ides, dois acantoc?falos e um pentastom?deo. Foram coletados 10.418 esp?cimes de endoparasitos, sendo que 6162 (59,15%) foram coletados de P. mesopotamicus, 1249 (11,99%) de P. fasciatum, 1173 (11,26%) de Z. zungaro, 1167 (11,2%) de P. corruscans. O t?pico padr?o de distribui??o agregada foi observado para todas as esp?cies, onde os pimelodideos analisados foram os que apresentaram maior diversidade de esp?cies, embora sem a presen?a de nenhuma esp?cie de endoparasito dominante. As rela??es do comprimento do corpo do hospedeiro entre a preval?ncia e a abund?ncia parasit?ria foram positivas para o parasitismo de P. lineatus por N. (N.) curemai e A. compactum, e de P.corruscans por S. oxycephala. Por outro lado, o parasitismo de P. corruscans por Porrocaecum sp. apresentou rela??o negativa entre a abund?ncia e o crescimento do hospedeiro. Em Z. zungaro apenas a abund?ncia de P. rugosa e Porrocaecum sp. apresentaram rela??o positiva com o comprimento total do peixe. O sexo dos hospedeiros influenciou significativamente a abund?ncia de N. (N.) curemai em P. lineatus, de S. spectatus em P. mesopotamicus e a preval?ncia parasit?ria de S. oxycephala em P. fasciatum, sugerindo a exist?ncia de diferen?as ecol?gicas e comportamentais entre hospedeiros machos e f?meas. A an?lise de agrupamento da similaridade entre as composi??es de endoparasitos dos peixes migradores resultou em 2 grupos principais bem diferenciados, com apenas 16,03% de similaridade entre eles. O primeiro grupo foi formado pelos peixes pisc?voros e o segundo, por peixes on?voros e detrit?voros. Entre os pimelod?deos analisados, a composi??o de suas comunidades endoparasit?rias apresentaram similaridade qualitativa de 50%, chegando a 87,5% entre P. corruscans e P. fasciatum. O Characidae S. brasiliensis apresentou 39,68% de similaridade qualitativa em rela??o ao grupo interno formado por Pimelodidae. No outro grupo principal, o Characidae on?voro P. mesopotamicus e o Prochilodontidae detrit?voro P. lineatus apresentaram 22,22% de similaridade na composi??o entre suas comunidades endoparasit?rias. Quanto a similaridade quantitativa, apenas um grupo principal foi formado. A similaridade entre os pimelod?deos foi de 50,35%, chegando a 67,29% entre P. faciatum e P. corruscans. Salminus brasiliensis compartilhou 30,46% de similaridade quantitativa entre os pimelod?deos e 12,41% com P. mesopotamicus, que, por sua vez, apresentou apenas 2,02% de similaridade quantitativa com P. lineatus. Dentre os peixes migradores de interesse comercial do Pantanal Norte Mato- Grossense, a similaridade na composi??o e estrutura de suas comunidades endoparasit?rias foi fortemente influenciada pela proximidade filogen?tica dos hospedeiros, assim como pelo h?bito alimentar exclusivamente pisc?voro, associado ? disposi??o dos peixes na coluna d??gua.