GASTRIC EVACUATION IN RUFFE (GYMNOCEPHALUS-CERNUUS (L)) AND THE ESTIMATION OF FOOD-CONSUMPTION FROM STOMACH CONTENT DATA OF 2 24H FISHERIESIN THE ELBE ESTUARY

The rate of gastric evacuation in ruffe Gymnocephalus cemnuus was stud ied at two different temperatures (14 and 19 degrees C) and with two d ifferent food types (chironomid larvae and Mysidaceae). Gastric evacua tion was described using an exponential model. The effects of temperat ure and fish size were incorporated in a multivariable version of the exponential model. The evacuation model was applied to estimate the da ily ration of ruffe using stomach content data obtained from two 24h f isheries performed in the Elbe estuary. Daily rations based on the gas tric evacuation model (for mysid or for chironomid prey) were estimate d at 1.3 % to 2.3 % (body wet weight) for adult ruffe and 2.3 % to 4.3 % for juveniles. The results are discussed with regard to the tempera ture adaptation of ruffe.