Diet composition and feeding habits of the African sharptooth catfish Clarias gariepinus (Burchell, 1822) from Ribb Reservoir, South Gondar, Ethiopia

A total of 525 catfish samples were collected with various fishing equipment, including hooks, longlines, and different mesh sizes of gillnets (4-12 cm). Out of these specimens, 379 (72.2%) stomachs contained prey items, whereas 146 (27.8%) were empty stomachs. Overall, fish prey, zooplankton, detritus and phytoplankton were the four most important food items, accounting for 48.1%, 21.8%, 17.1% and 5.9% of C. gariepinus diets by volume respectively. Diet composition varied across different size classes of the fish. The smallest fish (<37 cm standard length) mainly consumed detritus, mud (sediment), and zooplankton which comprise 41.2%, 29.3%, and 19.8% of the total volume, respectively. The larger fish (>37 cm SL) primarily fed on fish prey (14.0-74.1%) followed by zooplankton (11.2-21.3%) by volume. The relative importance of detritus, mud, zooplankton, phytoplankton, and insects decreased with increasing fish size from the Ribb Reservoir. The food and feeding habits of C. gariepinus significantly differed between dry and wet seasons. Fish prey and detritus were mainly consumed in the dry season and contributed to 63.6% and 21.9% of the total volume respectively. Zooplankton and phytoplankton were the most preferred food items during the wet season, contributing 71.8% and 22.2% of the total volume. Generally, C. gariepinus appears to be an omnivore, the species exhibits ontogenetic dietary shifts with larger specimens being more carnivorous, and the species exhibits dietary plasticity across wet and dry seasons, which may be linked to food availability from the Ribb Reservoir.