The spatial gradients created after the installation of large reservoirs produce a great diversity of biotopes, which affects the distribution and structuring of aquatic communities, mainly fish. Thus, we hypothesized that the fishes living in the lotic stretch (river zone, closest to the natural environment) of the reservoir would have lower overlap and higher niche breadth than fishes living in the lentic stretch. Samples were collected in six sections (lentic and lotic) of the Chavantes Reservoir, middle Paranapanema River. A total of 1478 individuals distributed in 13 species were sampled in both stretches. Many resources were acquired by species, and we observed that nine species present significant differences when comparing the two stretches. Furthermore, only \emph{Schizodon nasutus.