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

Abstract

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.