Composition and trophic structure of a fish community of a clear water Atlantic rainforest stream in southeastern Brazil

As part of a larger project that aimed to determine the factors that regula te fish productivity in a clear water river of the Atlantic rainforest, Sao Paulo State, Brazil, composition and the trophic structure of the fish com munity of the middle course of the river were studied from January 1995 to May 1996. Of the 17 species collected, Mimagoniates microlepis, Schizolecis guentheri, Phalloceros caudimaculatus and Kronichthys heylandi accounted f or 83.2% of the total fish abundance. Most of the species were insectivorou s (35.7%), followed by detritivores (21.4%), benthivores (14.2%), omnivores (14.2%), herbivores (7.1%), and piscivores (7.1%). Results of food overlap analysis as calculated by the Index of Morisita showed that 17.5% of the s pecies pairs overlapped. Habitat segregation, however was observed among mo st of the species, suggesting some degree of food partitioning. Despite the characteristics of this escarpment river, which produces spates year round , no seasonal variation in diet was observed, suggesting that although food abundance may fluctuate throughout the year, most items are in constant su pply. The importance of allochthonous food was considered and it appears th at, though only a few species feed on this source (including detritivores), they make up 87.2% of the total fish abundance. The low abundance of most of the fishes, the high number of endemic species and the strong dependence of the species on a few food resources suggest that these systems are sens itive to anthropogenic impacts and require future studies.