Interactions between Nile perch, Lates niloticus, and other fishes in LakeNabugabo, Uganda

The introduction of the predatory Nile perch, Lates niloticus, into the Lak e Victoria basin coincided with a dramatic decline in fish species richness and diversity. This study focused on interactions between Nile perch and i ndigenous fishes in Lake Nabugabo, Uganda, a small satellite lake of Lake V ictoria. We evaluated how the foraging impact of juvenile Nile perch on pre y fishes varied with the size of the predator. We also evaluated the role o f wetland ecotones in minimizing interaction between Nile perch and indigen ous fishes. Wetland ecotones in Lake Nabugabo were characterized by complex structure (e.g., dense vegetation) and lower dissolved oxygen levels than non-wetland (exposed) areas. Nile perch (8.6-42.2 cm, TL) were 3.7 times mo re abundant in offshore exposed areas than in inshore areas near wetland ec otones, and the proportion of Nile perch using wetland and exposed areas wa s independent of their body size. However, species richness was higher in w aters at wetland ecotones than in exposed areas. Nile perch (5-35 cm, TL) e xhibited a shift in diet at approximately 30 cm TL from feeding primarily o n invertebrates to piscivory. Although the shift to piscivory occurred at a pproximately the same body size for Nile perch from both wetland and expose d habitats, the shift to piscivory was less abrupt in Nile perch captured n ear wetland ecotones. Nile perch from wetland areas consumed a greater dive rsity and a larger percentage of fish prey than those from exposed sites. H owever, the low abundance of Nile perch in wetland ecotones suggested that interaction between predator and prey in these areas is much reduced.