GROWTH AND FOOD OF RUFFE GYMNOCEPHALUS-CERNUUS (L) IN THE ELBE ESTUARY

In summer 1991, ruffe of the Elbe River Estuary were investigated. Fem ales were found to have a L(infinity) of 26.1 cm TL and a W(infinity) of 279 g. Values for males were 23.3 cm and 193 g, respectively. The g rowth performance was comparatively good with P = 2.04 for females and a value of 1.97 for males. A comparison with literature data indicate s that ruffe growth performance has improved during the past decades. For the length class 16.5-20 cm (AG approx. III-IV) males were predomi nant, whereas for 20.5-22.5 cm (AG approx. IV-V) the females were dear ly more abundant. This indicates significantly better female growth. A ll animals larger than 23 cm were exclusively females. The food of ruf fe consisted chiefly of Neomysis integer, Crangon crangon, Osmerus epe rlanus and Gammarus zaddachi. For G. zaddachi and N. integer the prey size did not increase significantly with predator size. By contrast, a significant increase of prey size with fish size was found for C. cra ngon, and most conspicuously for O. eperlanus. The latter were taken o nly by ruffe larger than 17.5 cm. Smaller individuals were evidently u nable to feed on smelt.