Rivers show a longitudinal gradient from upstream to downstream, with consecutive changes in environmental characteristics and community composition. The main goal of this study was to describe the longitudinal variations in the characteristics of the fish fauna of Ceballos-Saldán River. Fish collection was performed at five sites along the river, before and after the main cities. Fish assemblages were described by specific composition, fish abundance, richness, diversity and dominance. These assemblage attributes were estimated for each sampling site. Species/abundance models were applied to each fish assemblage along the river. A total of 1,914 individuals were collected in Ceballos-Saldán River, which correspond to 17 species. Eleven of them were cited for the first time in the basin. The most abundant order was the Siluriformes. The most abundant species was Hypostomus cordovae (Günther, 1880). The only community attribute that significantly changed along Ceballos-Saldán River was total abundance, which presented its minimum value before Río Ceballos city. Three different species abundance models, along the river, described fish assemblages.
Fish assemblages; freshwater; species diversity; river
