FOOD, FEEDING HABITS AND POPULATION STRUCTURE OF “NINGU” (Labeo victorianus, BOULENGER, 1901) IN FOUR SELECTED RIVERS OF THE LAKE VICTORIA BASIN, KENYA.

Abstract

“Ningu” (Labeo victorianus Boulenger, 1901) is one of the endemic fishes in Lake Victoria Basin (LVB), but is now threatened by multiple stressors caused by human activities. This study investigated spatial and temporal variability in food composition and condition of Labeo victorianus in Awach, Mara, Nyando and Sondu-Miriu rivers of Lake Victoria, Kenya. Sampling was done during the dry and wet seasons by electrofishing. Food composition analysis showed that Labeo victorianus is a benthophagus and omnivorous species whose diet is dominated by detritus, plant material and insects. There were differences in food composition among rivers, with significant river X season interactions (PERMANOVA F = 11.6, df = 4, p = 0.001), suggesting that the diet depended on prevailing environmental conditions. In turbid rivers the diet was dominated by detritus while in less turbid rivers it was dominated by insects and periphyton. Sand and mud also formed a significant part of the diet, which was an indication of limited preferable food items. There were ontogenetic shifts in food composition (PERMANOVA F = 4.6, df = 3, p = 0.001), but also with a spatial interaction (PERMANOVA F = 5.6, df = 7, p = 0.001), further indicating the role of environmental conditions in determining the diet for different size classes. Interestingly, fish condition did not differ among rivers. Labeo victorianus population size structure was unimodal (7-15cm) in Awach, Nyando and Sondu Miriu rivers while bimodal in Mara River. This study shows that turbidity and organic matter and nutrient loading determine the diet of Labeo victorianus in LVB Rivers, and provides further justification for maintenance of water quality as a conservation measure for threatened species. The findings from this study can inform efforts to culture the species for restocking and/or food production. The findings also have greater implications for other fish species threatened by human activities, and can be used to inform sustainable management of riverine fisheries and conservation of threatened of Labeo victorianus in the LVB. Further studies to incorporate use of stable isotopes may be used to provide historical information on the food of the species.