FOOD HABITS AND DIEL FEEDING RHYTHM OF INTRODUCED FISH, T. ZILLII GERVAIS, 1948 (PISCES: CICHLIDAE) IN LAKE ZWAI, ETHIOPIA

Abstract

Food habits of adult Tilapia zillii was studied in Lake Zwai from samples collected over 12 months during the year 2001 using gillnets of 60 and 100 mm stretched mesh. Younger fish caught in October, November and December using beach seine of 5 mm stretched mesh were also studied for food composition. Feeding rhythm of the fish was assessed based on samples collected in October 2001 over 24-hour period at 4-hour interval. Food items identified from stomach contents were analysed using the frequency of occurrence and the points methods. Macrophytes, detritus, blue greens, diatoms, green algae, Ceratium, Euglena and Phacus constituted food of plant origin whereas chironomid larvae, Copepoda, Cladocera, Rotifera, Nematoda, fish eggs and fish scales constituted food of animal origin. Furthermore, animal foods such as Ephemeroptera and molluscs were noted in the diet of adult fish. In adult T. zillii, macrophytes occurred in all of the stomachs examined and composed 86% of the diet whereas 11% was contributed by phytoplankton. However, in young fish phytoplankton constituted the bulk of the diet (63%) followed by plant detritus (17%) and chironomid larvae (12%). The feeding pattern of T. zillii showed both diel and nocturnal rhythm; however, feeding was more intense during daytime.