FEEDING OF RUFFE (GYMNOCEPHALUS-CERNUUS) IN RELATION TO THE ABUNDANCEOF BENTHIC ORGANISMS IN LAKE VORTSJARV (ESTONIA)

From May till November 1994 the diet of ruffe was investigated in the shallow eutrophic Lake Vortsjarv (South Estonia). 187 ruffes of standa rd length (SL) of 4.3-12.0 cm were examined. Ruffe of SL over 4.5 cm ( age 1+ and older) were typical benthophagous fishes consuming mainly c hironomid larvae and pupae (over 95% of the weight of food). Chironomu s plumosus (91%), Einfeldia carbonaria (36%) and Microchironomus tener (31%) had the highest frequency of occurrence. The most important foo d item was C. plumosus (about 98% of the chironomid biomass in stomach s). The biomass of C. plumosus in the profundal mud bottom corresponde d to its proportional amount in stomachs of ruffe. The diet of ruffe w as compared with that of eel (Anguilla anguilla) and bream (Abramis br ama). Overlap in their diets appeared mostly in respect of C. plumosus larvae and pupae.