The Food and Feeding Ecology of Nile Tilapia, Oreochromis niloticus, in Lake Hayq, Ethiopia

Workiyie Worie Assefa, Abebe getahun


We investigated the food and feeding habits of Nile tilapia, Oreochromis niloticus, in Lake Hayq, Ethiopia from August 2008 to March 2009. A total 931 fish were collected by gillnets of various stretched mesh sizes, of which 326 individuals of Oreochromis niloticus stomachs contained food. The stomach contents were analyzed using frequency of occurrence, numerical methods and the Geometric Index of Importance (GII). The food items in the stomach covered a wide variety, ranging from various types of phytoplankton to zooplankton and to macrophytes. The major food items in terms of frequency of occurrence were Microcystis (87.7%), Cosmarium (65.13%), Navicula (64.2%) and Daphnia (71%) genera. Numerically, Cosmarium (38.5%) and Microsystis (31%) dominated the food of O. niloticus. However, Geometric Importance Index GII suggested that the most consumed group was Microcystis (83.93%). A monthly variation was also noted in the stomach contents of O. niloticus over the period of investigation. The food composition of O. niloticus showed slight variation among fish size. The contribution of zooplankton (Daphnia and Keratella) tended to increase with decreasing size of the fish, but Copepoda (Thermocyclops) tended to increase with size. Size based difference is also supported by one-way analyses of similarities (ANOSIMs) and the difference is mainly due to the differences in the importance of green algae (Cosmarium) and blue greens (Microcystis). This study is an important step towards understanding the food web in Lake Hayq, and eventually developing a trophic model for use in fisheries management.


Diet Composition; Feeding Habits; Food Items; Size Groups; Planktivorous; Geometric Importance Index


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