Gut Content Analysis and Feeding Relationships Reveal Low Competition for Food Resources in Non-Annual African Rainforest Nothobranchiid Assemblages

Understanding the trophic ecology of fish species is essential for developing effective management and conservation strategies. This study examined the role of diet in the assemblage structure of non-annual nothobranchiid fish species inhabiting permanent rainforest streams in southern Cameroon. In total, 1010 nothobranchiid individuals, assigned to 12 species belonging to two subgenera (mainly Aphyosemion), were harvested. The non-empty guts of 488 individuals were analysed, both qualitatively and quantitatively. All species examined were generalists. Their diet primarily consisted of terrestrial insects falling from the tree canopy, representing the bulk of their foraged food (%N = 76.8%), with an index of relative importance (IRI) of 94.3%. Hymenopterans were predominant in the environment (62%) and constituted the preferred prey type (IRI = 96.7%); the other items were accidental. Aquatic dipterans (Chironomidae) and Ephemeroptera followed. The diet of these fish species did not vary with parameters like site altitude, season, sex/ontogenetic groups, or fish size. They all fed on the same prey categories in equal proportions. The dietary overlap between the nothobranchiid fish species at sympatric occurrence sites was generally high, with a high reduction in their prey type uptake compared to a greater variety of prey intake in allopatric situations. Results suggest that there is low competition for food resources among these phylogenetically related species; they coexist by making immediate adjustments. In Cameroon rainforest streams, diet is not a factor structuring Nothobranchiid fish assemblages, providing valuable information for the ecological preservation of their biotope characteristics, which they rely on the most for survival.