PRELIMINARY STUDIES OF PROTEIN SYNTHESIS, GLUCONEOGENESIS AND LIPOGENESIS WITH LABELLED U 14C GLUTAMATE IN COHO SALMON: EFFECT OF SEA TRANSFER

This experiment was carried out in two groups of coho salmon (Oncorhynchus kisutch) hatched in early 1982 in Brittany (France). The biggest fish (group 1) had been kept in freshwater, although smoltification had been evident during autumn 1982. The smallest fish (group 2) had not smoltified. In April 1983, fish of group 1 resembled smolts (average weight about 300 g) again while those of group 2 looked like parr (average weight about 40 g). At that time, injections of U 14C glutamate were made intraperitoneally and measurement of the incorporation of 14C into protein, glucose and lipids of plasma, liver and muscle was performed after 2, 3 or 5 hours. This operation was repeated in June on batches of salmon out of group 1 that were transferred, either into seawater (SW) or freshwater (FW) tanks. At that time, the fish were either fully adapted to SW or “desmoltified” in FW. The results show in groups 1 and SW very clear modifications of the use of glutamate as compared with groups 2 and FW: gluconeogenesis is enhanced; apparent protein anabolism is enhanced in liver, but depressed in muscle. Apparent lipogenesis from glutamate is sharply decreased; therefore preparation for, and adaptation to, seawater induces clear changes in the intermediary metabolism. A second experiment was carried out in October 1983 in fish, where gill ATPase was measured to confirm that the modifications were due to smoltification itself. The effects of autumn smoltification are, however, very different from those observed in spring.