Tilapia esculenta is abundant in Lake Victoria, and is the most important food fish in this area. It has been stated1 that this fish feeds on phytoplankton. However, further investigations were undertaken, and the contents of stomach and rectum of the same specimen were examined and compared in a large number of fish taken at weekly intervals during the whole of 1950. A consideration of these results has led to the conclusion that only the diatom members of the phytoplankton are digested, whereas the Blue-Green and Green Algae pass undigested through the gut.