Trophic dynamics and morphometric divergence of coexisting neotropical cichlid species (Teleostei: Cichliformes) in relation to a dam.

Freshwater species are under threat from anthropogenic disturbance from in-stream barriers. Trophic interactions are a major driver of community structure and understanding how species partition resources in relation to barriers can help determine ecological impacts. In this study, we analyzed the diet based on stomach contents of three cichlid species from distinct genera and with divergent morphologies that occur in syntopy (Apistogramma piauiensis, Cichlasoma cf. zarskei, and Saxatilia brasiliensis) from the Mata de Itamacaoca, middle Munim River basin, Maranhão, northeastern Brazil, examining prey diversity and richness variations above and below a dam. Apistogramma piauiensis and Saxatilia brasiliensis primarily consumed insects, while Cichlasoma cf. zarskei had a more diverse diet, including insects, substrate, and fish. The dam had no measurable effect on stomach content diversity or richness; however, there were species-specific differences, with the diet of A. piauiensis showing lower prey richness than the other two species and lower dietary diversity than Saxatilia brasiliensis. nMDS and PERMANOVA analyses indicated considerable dietary niche overlap among species, with a weak but significant effect of species on the composition of consumed prey. There was a high dietary overlap between Cichlasoma cf. zarskei and Saxatilia brasiliensis. All species separated in morphospace with Saxatilia brasiliensis exhibiting traits related to predatory foraging. These results indicate niche separation in ecologies among the three focal species, which may be related to differences in morphology. However, given the limited temporal scale and variables assessed, further studies are necessary to comprehensively evaluate the influence of the dam on trophic resources and fish assemblages.