Zooplanktonic dietary preferences of <i>Ethmalosa fimbriata</i> (Clupeidae) and <i>Eucinostomus melanopterus</i> (Gerreidae) in Lake Nokoué in Benin

The aim of the present study was to examine the zooplanktonic prey preferences of two important artisanal fish species, Ethmalosa fimbriata (Clupeidae) and the Eucinostomus melanopterus (Gerreidae) in Lake Nokoué. A monthly sampling was conducted from September 2021 to January 2022, and the stomach contents of the sampled fish were analyzed using presence-absence and numeric abundance methods. The results revealed that both species primarily consume three main zooplankton taxa: copepods, rotifers, and cladocerans. Ethmalosa fimbriata, especially individuals subadults (9-13 cm) consistently favored Copepods, with an occurrence frequency of 70.45%, regardless of its size. In contrast, Eucinostomus melanopterus, especially adult individuals (13-15 cm), exhibited a strong preference for Cladocerans, with an occurrence frequency of 50.54%. The monthly variation in the Average Nutrition Index (ANI) for E. fimbriata showed higher feeding intensity during November (5.9 ± 5.0) and lower in January (1.92 ± 1.2), with a significant difference (P-value<0.05). Principal Component Analysis indicated no significant zooplankton prey preference based on size among juvenile stages of E. fimbriata. However, adult E. melanopterus demonstrated a discernible selectivity towards Cladocerans. These findings, with significant size-dependent variations (P-value<0.001), provide valuable insights into the dietary preferences and ecological roles of these two fish species in Lake Nokoué.