Composition and diversity of the fish assemblages under influence of a gradient

The structure of ichthyofauna is determined by several factors involving environmental characteristics that modify along the gradient river dam. The aim of this study was to compare the ichthyofauna distribution of a subtropical dam tributary in four distinct stretches along the river/dam gradient. The samples were carried out quarterly during a year using gill nets, trawling, and sieves with a standardized capture effort to capture fish. The ichthyofauna of the tributary presented 41 species with 4,598 individuals. Three non-native species were recorded. The richness of species did not show significant difference among the stretches, although Shannon–Wiener diversity and evenness showed significant variations among the stretches. The distribution ordination (partial CCA) showed greater correlation between fish assemblage and impacted composition of surroundings. This study approaches the existence of an environmental gradient within the river mouth, influenced by a reservoir and the variations of the fish assemblage