The food and feeding habit of Oreochromis niloticus L. (Pisces: Cichlidae) in Lake Chamo, Ethiopia

The food of Oreochromis niloticus in Lake Chamo, Ethiopia was studied from the stomach contents of 449 adult (290B570 mm total length, tl) and 145 juvenile (61B115 mm tl) fish. O. niloticus was found to be essentially phytoplanktivores in Lake Chamo, and the composition of the phytoplankton diet varied seasonally. The diet of both adult and juvenile fish consisted of 10 genera of blue greens whereas green algae and diatoms each contributed 8 genera. Blue greens as a group contributed the bulk of the diet of adult fish. The most frequently encountered genera from the blue greens were Anabaena (96B100), Lyngbya (85B100), Microcystis (81B100) and Oscillatoria (41B100). Cosmarium (79B100) from the green algae and Navicula (82B100) from the diatoms were also frequently observed. In terms of percentage composition by number, the blue greens contributed over 60% of the total food ingested. Of these, more than 50% was due to Anabaena, Lyngbya and Microcystis. Zooplankters occurred on rare occasions in the stomach contents of both adult and juvenile fish. The feeding pattern of adult O. niloticus was observed to have a diel rhythm. O. niloticus in Lake Chamo is a continuous feeder during the day and peaked at 16 hr. Daily ingestion of phytoplankton was estimated to be about 3.7% of its wet body weight at an average water temperature of 26E C. SINET: Ethiopian Journal of Science Vol. 23, No. 1 (June 2000), pp. 1-12 Key words/phrases: Ethiopia, Food, Lake Chamo, Oreochromis niloticu