This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/ dry). A thermal gradient separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal) than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches. Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam disruption and flood increased connectivity to the lotic systems.

ABSTRACT. Diversity of fish assemblages in the four geographic units of the Paraíba do Sul river. Diversity patterns of fish assemblages along the four geographic units (upper, middle-upper, middle-lower and lower reaches) of the Paraíba do Sul river were studied aiming to assess spatial (geographic units) and seasonal (wet/dry periods) variations. Twenty-five sites were sampled between December 2002 and March 2003 (summer/wet) and, August to November 2003 (winter/dry). Fish were caught by a standardized effort, using gill nets, cast nets and mesh trays. A total of 81 species were recorded comprised in 9 orders, 29 families and 55 genera. Characiformes showed the highest number of species (28) followed by Siluriformes (23). Perciformes, mainly Tilapia rendalli and Geophagus brasiliensis, and Cyprinodontiformes, mainly Poecilia vivipara and Poecilia reticulata, were the most numerically abundant groups, while Siluriformes, mainly Hypostomus luetkeni, and Perciformes, mainly Geophagus brasiliensis showed the highest biomass. Poecilia vivipara was recorded only in dry period. Spatially, Hoplosternum littorale predominated in the middle-upper reaches, Pimelodus fur, Hypostomus luetkeni, Glanidium albescens in the middle-lower, and Loricariichtys spixii and Prochilodus lineatus, in the lower reach. Number of species and Margalef's richness showed an increase from the upper to the lower river reaches, mainly during the wet period. Species widely distributed along all over the river extent (G. brasiliensis, Oligosarcus hepsetus e P. reticulata) are opportunistic and can use the available resources despite poor environmental conditions, reflecting the state alteration of the river. Differentiation on the physiography throughout the longitudinal extent of the basin does not match shifts in fish assemblages, suggesting that factors associated to habitat alterations could be structuring fish community at local scale. KEYWORDS.Fish assemblages, spatial patterns, fish distribution, ichthyofauna, neotropical rivers. espécies e a riqueza de Margalef apresentaram um aumento do trecho superior para o inferior, principalmente durante o período de cheia. Espécies que apresentaram ampla distribuição ao longo do rio (G. brasiliensis, Oligosarcus hepsetus e P. reticulata) são consideradas oportunistas por se aproveitarem dos recursos disponíveis em ambientes pobres, refletindo o estado de alterações do rio. Diferenciações na fisiografia ao longo da extensão longitudinal da bacia não coincidiram com mudanças nas assembléias de peixes, sugerindo que fatores associados a alterações de hábitats poderiam estar estruturando a comunidade de peixes a nível local. PALAVRAS-CHAVE.Assembléias de peixes, padrões espaciais, distribuição de peixes, ictiofauna, rios neotropicais.O rio Paraíba do Sul é um dos mais utilizados sistemas lóticos do Brasil, por situar-se entre os maiores centros urbano-industriais do país, e tem sofrido alterações de origem antrópica ao longo dos últimos quatro séculos. A intensa urbanização e industrialização são os mai...

The Paraíba do Sul river is located in one of the most developed part of Brazil and receives many organic and industrial effluents directly affecting the ichthyofauna. Concentration of four heavy metals (Cu, Cr, Zn and Pb) were determined in two tissues (muscle and gonads) of three abundant fish species from different trophic levels (Oligosarcus hepsetus-carnivore, Geophagus brasiliensis-omnivore and Hypostomus luetkeni-detritivore) between November 2002 and April 2003. The aim was to test the hypothesis that the trophic level and the proximity from impacted areas influence levels of contamination and to assess if these species are indicators of large-scale habitat quality. Levels of heavy metals were detected by Total Reflection X-ray Fluorescence with Synchrotron Radiation (SR-TXRF) at the Brazilian National Synchrotron Radiation Laboratory (LNLS). Generally, gonads showed higher metal concentration than muscles, except for Cr. All examined metals, but Cu, exceeded the maximum permitted concentration (mpc) by the Brazilian legislation for human consumption in at least one tissue. O. hepsetus (carnivore) showed the highest contamination levels, followed by G. brasiliensis (omnivore) and H. luetkeni (detritivore). The middleupper segment, which encompasses large urban areas, showed the highest levels of metal contamination in most cases. O. hepsetus showed the highest levels of contamination in muscles for Pb in the middle-upper river segment (7.98±3.73; mpc=2.0 μg g −1 ) and for Cr in the upper (5.53±0.05; mpc=0.10 μg g −1 ) and middle-upper (4.20±0.85; mpc=0.10 μg g −1 ) segments, which indicates that human population should avoid to consume these fishes species from these segments of the Paraíba do Sul river.

International audienceFish communities and habitat structures were evaluated by underwater visual censuses a rocky location impacted by thermal discharge (I) and at two control locations, one in a bed (C1) and the other in a rocky shore with higher structural complexity (C2). Habitat indicators and fish communities exhibited significant differences between the impacted and control locations, with the impacted one showing a significant decrease in fish species richness and diversity, as well as a decrease in benthic cover. At the I location, only 13 fish species were described, and the average water temperature was 32 ± 0.4 °C, compared with 44 species at C1 (25.9 ± 0.3 °C) and 33 species at C2 (24.6 ± 0.2 °C). Significant differences in fish communities among locations were found by ANOSIM with , sp and typical of location I, while and were typical of the control locations. Our study shows that thermal pollution alters benthic cover and influences fish assemblages by altering composition and decreasing richness

We collected fishes and environmental variables in three zones (upper, middle and lower) of a small open tropical estuary during flood tide. The aim was to test for differences in fish assemblages along a gradient from freshwater to marine waters and to detect any seasonal variation in fishes and environmental variables across these zones. A total of 111 species (18 in the upper, 50 in the middle and 66 in the lower estuary) were recorded, forming three distinct fish assemblages, with the family Eleotridae dominating in the upper, Gerreidae in the middle, and Sciaenidae in the lower estuary. Only two species (Geophagus brasiliensis in the upper and the middle zones, and Eucinostomus argenteus in the middle and the lower zones) composed more than 1% of the total number of individuals in more than a single zone. Short‐term (tidal) changes in salinity in the middle estuary were associated with different assemblages in the three estuarine zones, even in winter, when the differences in salinity are lowest between the middle and the lower zones. Seasonal variation in salinity was irrelevant, except in a protected sidewater lagoon in the middle estuary. Low salinity seasonal change may be related to the lack of seasonal variation in the structure of fish assemblages in all estuarine zones.