<b>Contribution of different mesohabitats to the maintenance of fish richness and diversity in the lower Preto River

Resumo

The presence of different mesohabitats in freshwater systems can support higher local and regional fish richness. Thus, their suppression by dam-building represents a real threat to aquatic biodiversity. Our aims were: (1) to survey the fish fauna in two different mesohabitats in lower Preto River: a riffle indirectly threatened by dam-building and a run with different physical structure; and (2) to analyze and compare the fish community structure in these different mesohabitats. Six samplings were made during one year in two reaches (R1 and R2). We conducted a ‘one way’ ANOSIM to assess the differences in fish community structure between R1 and R2. Fifty-three species were recorded, with the occurrence of Aphyocheirodon hemigrammus and Myleus tiete, two Brazilian threatened species. The highest richness was observed in R2. Nevertheless, diversity and evenness were significantly higher in R1. Rheophilic species were more common and restricted to R1 and species typical of lentic environments were predominant in R2. Fish community structure was different between R1 and R2 (R = 1, p = 0.02). Our results demonstrated that mesohabitats mosaic through rivers can contribute to the maintenance of a diverse fish assemblage.