Trophic niche differentiation in the African elephant fish community (Mormyridae) from the Sanaga River in Cameroon

Abstract Multiple species of the elephant fishes (Mormyridae) commonly coexist in sympatry in most African tropical rivers and lakes. In this study, we investigated the trophic ecology and potential trophic niche partitioning of eleven mormyrid fish species from the Sanaga River system (Cameroon) using the stable isotopes of carbon and nitrogen of muscles and of trophic prey samples. Albeit mormyrids mainly feed on invertebrates, we found differences in isotope signals and the trophic niche partitioning in the studied species. We further show that species with elongated snout tend to show higher carbon and nitrogen isotope signals, suggesting a potential role of snout shape in their trophic preferences. Furthermore, we found significant differences in isotopic signatures within the Mormyrus genus, highlighting ecological niche diversification among three closely related species. We also report on different isotopic signals between seasons of the year in four species, possibly caused by species migration and/or anthropogenic agricultural activities. Overall, our research presents robust evidence of the trophic niche partitioning within the entire mormyrid species community, shedding light on the enigmatic evolutionary history of these fascinating African fishes.