Influence of the changing environment on food composition and condition factor in Labeo victorianus (Boulenger, 1901) in rivers of Lake Victoria Basin, Kenya

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. We investigated spatial and temporal variability in food composition and condition of L. victorianus in influent rivers of Lake Victoria, Kenya. Sampling was done during the dry and wet seasons by electrofishing. Food composition analysis showed that L. victorianus is a benthophagus and omnivorous species whose diet is dominated by detritus, periphyton 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 a limited occurrence of 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, the fish condition did not differ among rivers. This study shows that turbidity and organic matter and nutrient loading determine the diet of L. victorianus in LVB rivers, and provides further justification for the maintenance of water quality as a conservation measure for threatened species.