The food, feeding habits and distribution of a siluroid catfish, Bagrus docmac (Forsskal), in the Kenya waters of Lake Victoria

Abstract

Adult Bagrus docmac in the Nyanza Gulf of Lake Victoria feeds mostly on fish–Haplochromis spp. and Engraulicypris argenteus (Pelligrin). Juveniles prefer aquatic benthic invertebrates with Phyllogomphus aethiop.?(K.elys), Phanostoma senegalense(Brauer), Chironomus spp. and Caridina nilotica (Roux) dominating, followed by Chaoborus spp., Povilla adusla (Navas), Valvata spp. and Neoperla spio (Newman) in order of importance. B. docmac exhibits diurnal changes in feeding habits. It feeds actively during dusk and dawn, taking advantage of the twilight environment for successful feeding mission–a crespuscular feeding behaviour. Selectivity of food seems dependent on occurrence of prey items. The species has an ubiquitous distribution in the Gulf but occurs more frequently with increasing water depth and decreasing water temperature. The biomass of the predator shows little correlation with water conductivity. Bagrus docmac and the other important piscivorous species in the lake, Lates niloticus (L.), are mutually exclusive in their bathymetric distribution within the Gulf. They also have different preferences for water temperature and conductivity.