GRADUAL TRANSFER TO SEA-WATER OF RAINBOW-TROUT - EFFECTS ON LIVER CARBOHYDRATE-METABOLISM

The levels of glycogen and glucose, as well as of the activities of se veral key enzymes of glycogenolysis, glycolysis, gluconeogenesis and t he pentose phosphate shunt were assessed in livers of small (97 g) and large (166 g) rainbow trout Oncorhynchus mykiss during gradual transf er to sea water (salinities of 0, 9, 18 and 28 parts per thousand). Pl asma glucose and protein levels were also evaluated. Liver carbohydrat e metabolism changed during gradual adaptation of rainbow trout to sea water. Glucose increased with salinity in livers of bath sizes of ani mals, as did glycogenolysis and gluconeogenesis, but this latter only in large animals, and glycolytic rates in small animals. The different responses in metabolic parameters between sizes of animals may reflec t a higher stress of the small animals and/or a better adaptation of l arge animals to increased salinities, in a way similar to that previou sly suggested by other authors after evaluation of non-metabolic param eters. The changes observed at 28 parts per thousand can also be the r esult of reduced food consumption. (C) 1995 The Fisheries Society of t he British Isles