The feeding periodicity and dietary changes of Haplochromis graueri, H. olivaceus, H. nigroides and H. kamiranzovu, 4 endemic species from lake Kivu, were investigated by determining the stomach fullness index at intervals of 3 hours over a 24-hour cycle. These 4 species showed 2 types of daily feeding activity rhythm both characterised by a major food intake at daytime. A first type of bimodal feeding rhythm with the first peak situated in the morning between 6.00 a.m. and 12.00 a.m. and a second one in the evening between 3.00 and 9.00 p.m. characterizes H. graueri, and H. olivaceus. H. kamiranzovu and H. nigroides on the other hand showed a unimodal feeding rhythm with a single peak situated in the afternoon between 3.00 and 6.00 p.m. The beginning of each period of active foraging is rather easily detected in catches by a rapid rise in number of fish captured. The highest degree of stomach fullness appears almost invariably about 3 hours after the beginning of such a foraging peak. The variation of the coefficient of vacuity in the various Haplochromis species studied is not only related to the dial feeding rhythm but also to the items ingested : it is higher in carnivorous species and lower in omnivorous, detritivorous and phytophagous ones. The relation between the uptake of various prey types and feeding time over the 24 h period indicates that some prey items are more accessible at specific hours of the day. These Haplochromis species have developed a strategy for cropping potential food items at specific periods of the day. This probably leads to a further reduction or in some cases to a complete absence of interspecific food competition.
