Some Aspects of the Feeding and Reproductive Biology of Oreochromis Niloctus L. (Pisces: Cichlidae) in Alwero Reservoir, Gambella Regional State, Ethiopia

Nile tilapia, Oreochromis niloticus, is economically one of the most important fish species in Ethiopia. Fish samples were caught using gillnets with 6 cm, 8 cm, 10 cm, 12 cm and 16 cm stretch mesh size. All the nets were set in the late afternoon between 4:00 5:00 pm and retrieved the next morning between 8:00 and 9:00 am. at nine occasions during the wet and dry seasons between September 2012 and March 15. Biological information such as condition factor, food habits, and length-weight relationships are useful for management of fish resources. The sex ratio showed preponderance of females over males (Chi-curvilinear relationship between total length and total weight of O. niloticus in the reservoir (Y= 0.052X2.76 and R2 = 0.947). This suggests that the fishes grow isometrically. There was no variation was observed in the condition of fishes between the wet and dry seasons. The size at first maturity (L50) of O. niloticus in Alwero Reservoir (male and female combined = 22.50 cm). In Alwero Reservoir phytoplankton species such as anabena and melosera were the major food items for O. niloticus.