The distribution and feeding ecology of the characid Brycinus sadleri in Lake Nabugabo, Uganda: implications for persistence with Nile perch (Lates niloticus)

Coincident with a rapid increase in numbers of introduced predatory Nile perch (Lates niloticus) in lakes Victoria, Kyoga, and Nabugabo of East Africa was a dramatic decline in populations of many native fishes. However, a few species, including the characid Brycinus sadleri, have shown remarkable resilience. This study examined how the distribution and foraging behaviour of B. sadleri in Lake Nabugabo may facilitate their persistence with Nile perch. Both B. sadleri and Nile perch were most abundant in exposed areas offshore (20m) as opposed to wetland areas. However, we found evidence for a strong diel shift in activity and modest changes in the habitat use of B. sadleri that may contribute to persistence with Nile perch. In general, B. sadleri actively foraged during the daylight hours and remained quiet during the night. Nile perch began foraging during the early evening and were more active during the night than during the day. By early morning the proportion of full stomachs in Nile perch was low, though there was evidence of a low level of feeding activity during the day. Stomach contents of Brycinus sadleri indicated a shift from surface to benthic feeding as light levels increased, which appears to decrease their susceptibility to predation by Nile perch during the daylight hours.