Food and feeding habits of Haplochromis (Teleostei : Cichlidae) from lake Kivu (Central Afrika). II. Daily feeding periodicity and dietary changes of some Haplochromis species under natural conditions.

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.