THE EFFECT OF GRADUAL TRANSFER TO SEA-WATER ON MUSCLE CARBOHYDRATE-METABOLISM OF RAINBOW-TROUT

An assessment of the levels of glycogen and glucose, as well as of the activity of several key enzymes of glycogenolysis, glycolysis, glucon eogenesis and the pentose phosphate shunt were performed in white and red muscle of rainbow trout (Oncorhynchus mykiss) of two different siz es, 97.03 +/- 3.03 g (small, n=67) and 165.69 +/- 5.01 g (large, n=68) during gradual transfer to sea water using salinities of 0, 9, 18 and 28 ppt. The results indicate the existence of changes in carbohydrate metabolism in both white and red muscle. Glycogenolysis was observed for both types of muscle associated with increased salinity. The gluco se obtained from glycogen breakdown appears to be used in situ in the white muscle of both sizes of animal through increased glycolysis, thi s is also the case for the red muscle but only for small animals. In n either white or red muscle, were major changes detected in gluconeogen esis, the pentose phosphate shunt or in the use of exogenous glucose. The metabolic changes described are indirectly related to the increase d energetic demand occurring during adaptation of rainbow trout to sea water. No main differences were observed between size for the paramet ers studied except in red muscle probably reflecting a better adaptati on of large animals to sea water.