Distribution and feeding of two sympatric species of piranhas Serrasalmus maculatus and Pygocentrus nattereri (Characidae, Serrasalminae) of the Ibicuí river, State of Rio Grande do Sul, Brazil

Abstract

Two species of piranhas occur in the Ibicuí River, one of the main tributaries of the Uruguay River in southern Brazil, Serrasalmus maculatus Kner, 1858 and Pygocentrus nattereri Kner, 1858. In order to analyze the distribution and feeding habits of these species we conducted collecting expeditions from December 1999 to January 2002, using a variety of fishing gears in three sites along the river, both in lentic and lotic habitats. A total of 203 individuals of S. maculatus and 86 of P. nattereri were caught, mostly in lentic habitats and closer to the Uruguay River, were P. nattereri seems to be more concentrated. The number of individuals captured at different times did not show variation in P. nattereri while the number of S. maculatus captured at mid-night was the highest. Young S. maculatus (2-4 cm standard length) fed mainly on fish fins and insects. Fish was the predominant item in remaining size classes for both species, with intra- and inter-specific overlap in larger classes (8-16 cm and >16 cm standard length). No differences in the repletion index between day time or habitats, were observed for the two species.