THE EFFECT OF SEAWATER TRANSFER IN LIVER CARBOHYDRATE-METABOLISM OF DOMESTICATED RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

1. A study of the levels of glycogen and glucose, as well as the activ ities of glycogen phosphorylase (GPase), glycogen synthetase (GSase), fructose 1,6-bisphosphatase (FBPase), phosphofructokinase (PFK), gluco se 6-phosphate dehydrogenase (G6PDH), pyruvate kinase (PK) and lactate dehydrogenase (LDH) was carried out in livers of domesticated rainbow trout (Oncorhynchus mykiss) of two different weights [small (80 g) an d large (140 g)) after transfer to seawater (28 p.p.t.) for 21 days. 2 . The results indicate that metabolic changes during adaptation of rai nbow trout to seawater appear to occur in two stages which, in additio n, appear to be size-dependent. 3. During the first stage a clear glyc ogenolysis (associated with an increase in GPase activity and a decrea se in GSase activity) and hyperglycemia were observed both in small an d large animals, being higher in the small ones. 4. A seeming increase in gluconeogenesis (as indicated by the activation of FBPase activity ) was observed only in large animals. 5. The mobilization of energy re serves could be associated with the increase in energetic demand of th e osmoregulatory organs. On the other hand, the second stage indicates that a successful adaptation to seawater did not occur, since the ani mals ceased to feed from day 7 of the experiment onwards.