AN EXAMPLE OF DIEL FEEDING CYCLE OF 2 PERCIDS, PERCH (PERCA-FLUVIATILIS) AND RUFFE (GYMNOCEPHALUS-CERNUUS) IN EUTROPHIC LAKE AYDAT (FRANCE)

Diel information on the dietary preferences of adult perch (Perca fluviatilis) and ruffe (Gymnocephalus cernuus) were reported, in relation to their feeding rythms. The gut contents of 47 perch (1+ to 5+) and 54 ruffe (2+ to 5+) were examined in terms of composition and fullness at 4 hours intervals on 20-21 July 1988. Globally, catch and feeding of perch was diurnal. The maximum feeding activity of each age classe was observed at the end of the afternoon. In contrast, the catch and feeding of ruffe were nocturnal. 1+ perch exerted a selective predation on Acanthodiaptomus denticornis : more than 1.2 g dry weight of this calanoid was eliminated by each kg fresh weight of fish during 24 hours. Perch 2 and ruffe (for all age classes) consumed insects larvae and pupae. Some individuals of P. fluviatilis greater-than-or-equal-to 2+ were piscivorous and cannibalistic. Most of the perch 2+ and older and all ruffe fed on macroinvertebrates; a large proportion ate Chironomidae larvae and pupae, with temporal segregation.