Dry Season Feeding Profiles of a Characiformes Assemblage in a Brazilian Tropical Stream

Trophic interactions between fish and their resources depends on resource availability and interspecific competition. To understand dry-season trophic profiles of a speciose Characiformes assemblage, we performed stomach content analysis to describe diet and determine levels of niche partitioning and morphological adaptations among eight Characiformes species in the dry season in Mata de Itamacaoca, Chapadinha Municipality, State of Maranhão, northeastern Brazil. Insectivory dominated most diets, with Astyanax cf. bimaculatus and Characidium cf. bimaculatum exhibiting the broadest niches. Specialization occurred in Curimatopsis cf. cryptica (85.07% plant material), and there was significant dietary segregation, with indicator species analysis linking Astyanax cf. bimaculatus to piscivory and Knodus guajajara to vermivory. Pianka's index revealed a wide gradient of trophic niche overlap, with the highest overlap observed between Hyphessobrycon piorskii and Knodus guajajara (0.95), and between Holopristis cf. ocellifera and Nannostomus beckfordi (0.96). Morphological PCA associated traits with feeding strategies, including caudal fin length (Astyanax cf. bimaculatus), body depth (Curimatopsis cf. cryptica), and oral gape width (Bario oligolepis). Mixed models confirmed insects and plant material, with a marginally significant effect, as key drivers of dietary variation. Therefore, the assemblage shows high niche overlap combined with diverse trophic profiles. The results demonstrate how dry-season resource scarcity promotes trophic divergence via morphological specialization, with generalists (Astyanax cf. bimaculatus) coexisting with specialists through niche partitioning, which is critical for conservation in this threatened urban-protected area.