Title : 1 Trophic niche differentiation in the African elephant fish community ( Mormyridae ) from the Sanaga 2 River in Cameroon 3 4

24 The elephant fishes (Mormyridae) are a diverse family of African freshwater fishes primarily inhabiting 25 tropical and subtropical riverine habitats with a general preference for invertebrate prey. Despite the 26 coexistence of multiple species within these habitats, specific details regarding their trophic specializations 27 remain unclear. In this study, we investigated the trophic ecology and potential trophic resource partitioning 28 of eleven mormyrid fish species from the Sanaga River system (Cameroon) using the stable isotopes of 29 carbon and nitrogen of muscles and trophic prey samples. Albeit mormyrids typically display an 30 invertebrate-based diet, we found variations in isotope signals among some species, and in some cases also 31 across different seasons. Species with elongated snout tend to show higher carbon and nitrogen isotope 32 signals compared to those without snout protrusion, suggesting a potential role of snout shape in their 33 trophic ecology. Notably, three species, Marcusenisus mento, M. sanagaensis and Paramormyrops batesii 34 have a lower trophic position than all the other mormyrid species (Campylomormyrus phantasticus, 35 Hippopotamyrus castor, Mormyrops anguilloides, M. caballus, Mormyrus tapirus, M. sp. “short snout”, M. 36 sp. “long snout” and Petrocephalus christyi). Furthermore, significant differences in isotopic signatures 37 were observed among three closely related species of the Mormyrus genus, highlighting ecological niche 38 diversification. This again may be linked to variations in snout protrusion length in these three species (two 39 of them undescribed). Additionally, we detected seasonal impacts on δC values, and to a lesser extent on 40 δN, particularly in the comparison of peak wet and dry season samples with those from the transition 41 phase between seasons. Possible explanations for these differences include species migration and/or 42 anthropogenic agricultural activities. Our study provides valuable insight into the trophic ecology of this 43 understudied group of tropical fishes by leveraging stable isotope analysis. We present evidence of niche44 partitioning within the species community, and our data could be relevant for future studies on stomach 45 content surveys, (micro)habitat preference, behavioral observations or life-history investigations of 46 mormyrid fishes in this region. 47 48

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