Temporal trophic shifts and feeding diversity in two sympatric, neotropical, omnivorous fishes: Astyanax bimaculatus and Pimelodus maculatus in Rio Tibagi (Paraná, Southern Brazil)

Abstract

In this study, we explored whether the two dominant, morphologically divergent, omnivores, Astyanax bimaculatus (Characidae) and Pimelodus maculatus (Pimelodidae) in the high diversity (>100 species) fish assemblage of the Neotropical Rio Tibagi (southern Brazil) exhibited full overlap in the use of feeding resources similar to those reported for closely related species in Rio Amazonas. Monthly feeding patterns were assessed in two years of contrasting hydrological conditions and were compared with those reported for other, allopatric populations within their distributional range. Astyanax and Pimelodus fed at all trophic levels and exhibited an acute ability to shift prey as a response to environmental variations or food shortage. Although aquatic and terrestrial insects and seeds of native and introduced plants were the major food items, spatial separation across the water column and ecomorphological constrains seem to prevent a simultaneous use of the same food items by the two species. Except when cultivated seeds (i.e. maize) were most abundant after harvest, overlap in the use of feeding resources was negligible, if any. We suggest that the assessment of trophic relationships in Neotropical fish assemblages require more detailed studies than those actually available.