Feeding selectivity of Oreochromis niloticus in Lake Naivasha and Oloiden in the Rift Valley, Kenya

An increase in the water level occurred in the Lake Naivasha leading to its merging with Lake Oloiden. The presence of Nile tilapia that is exploited commercially in the Lake Oloiden post water level rise is important. Study’s main focus was to investigate the feeding selectivity of Oreochromis niloticus post water level raise in the Lakes Oloiden and Naivasha. The lake depth and secchi depth were measured and Nile tilapia was sampled monthly for one year and analysis (300 fish) was done for the feeding selectivity of O. niloticus.  The food items that were present in the gut of fish in both lakes were: algae, detritus, other plant material, fish parts and zooplankton. An ontogenic shift was seen; juvenile fish consumed a higher percentage of zooplankton as compared to adult fish. The insects were not part of the fish’s diet as previous (before water level rise) in the Lake Naivasha. Nile tilapia feeds during the day and food selection was affected by seasonality. The fish in both lakes were in a good condition and the fullness index and the vacuity index varied; although, no variation was noted with sex nor maturity stage. Nile tilapia diversified its diet and took advantage of new environment (Lake Oloiden). The fish in the Lake Oloiden have similar feeding selectivity with those in Lake Naivasha. Further research should be done on feeding selectivity of small sized fish.