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Abstract
The food and feeding habits of five economically important fresh-and brackish-water fishes, Channa obscura, Chrysichthys nigrodigitatus, Heterotis niloticus, Synodontis nigrita and Trachinotus maxillosus, were investigated. A number of techniques were used to carry out gut content analysis, including the Hynes 'point' system based on volume estimations expressed as relative percentages. Juveniles of C. nigrodigitatus were omnivorous, consuming 32% gastropods, 30% nematodes, 14% diatoms and 8% crustaceans, while adults were planktotrophic, consuming 23% diatoms, 33% Chlorophyceae and 22% crustaceans. Synodontis nigrita juveniles fed almost exclusively (91%) on nematodes, while adults were predominantly planktotrophic, their diet comprising 50% diatoms and 50% crustaceans. Trachinotus maxillosus was exclusively benthotrophic, consuming 99.5% gastropods and 0.46% nematodes. Heterotis niloticus was planktotrophic at the adult stage and consumed 72% crustaceans, 12% gastropods, 3% fish and about 90% planktotrophic at the juvenile phase. Chrysichthys obscura was purely benthotrophic at the juvenile stage, feeding 100% on nematodes, but fed mainly (89%) on fish at the adult stage.