Food is the main axis of niche partitioning among fishes, being an important factor for the organization of their populations. We herein investigate this premise for two closely related species, by characterization and comparison of the natural diet of two heptapterid fishes, Rhamdioglanis transfasciatus and Rhamdia quelen along the Macaé River, Rio de Janeiro state, Southeastern Brazil. R. quelen was classified as carnivore, and the most important items of its diet were crustaceans and fishes. R. transfasciatus was classified as invertivore, as it ate mainly trichopteran and dipteran larvae. The calculation of the trophic position algorithm showed that both species are secondary consumers, but R. quelen had a slightly higher value. Both species can be considered as generalists but with differences of feeding strategies: some individuals of R. quelen behave as specialists, whereas most individuals of R. transfasciatus population act as generalists. Intraspecific comparisons revealed a similar diet of each species between the two sampling sites, however, the niche overlap between the populations of the two species was very low in the sites where both occurred, indicating the existence of resource partitioning between Rhamdia quelen e Rhamdioglanis transfasciatus in Macaé river.
feeding; niche; resource partitioning; Rhamdioglanis transfasciatus; Rhamdia quele
