RESUMO
In order to simulate the catadromous migration environment of the juvenile salmon (Oncorhynchus keta), five experimental groups containing different salinities (0, 5, 10, 15 and 20) were set up. The juvenile salmons with average body mass of (26.57 +/- 6.32) g and average full length of (14.44 +/- 1.05) cm were cultured for 130 days, and then the haematological biochemistrical indices was analyzed and the structure of liver tissue was observed to investigate the changes in physiological indices during the catadromous migration of juvenile salmon. The results showed that serum osmolality and the concentration of Na+, Cl- illustrated the same tendency with water salinity variation. Specifically, the serum Na+, C- and Mg2+ levels in the salinities of 15, 20 were significantly different from those in the salinity 5 and the freshwater and serum K+ in different salinities were all obviously lower than that in the freshwater. Also, the blood glucose level in salinity 10 was significantly higher than that in salinity 5 and 20, whereas total serum protein (TP), albumin (ALB) and globulin (GLB) levels all declined with the increase of salinity and the serum TP and GLB content in the freshwater group was remarkably higher than those in the salinity 15 and 20. There also existed an obvious discrepancy on total bile acids in freshwater group and the other salinity groups. The alanine aminotransferase (ALT) activity and aspartate aminotransferase (AST) activity in fresh water group were far different from those of the high salinity groups. Furthermore, in the low salinities (0 and 5), the liver cells of juvenile chum salmon partly broke down, and liver tissue was serious vacuolization. Collectively, the growth and survival rate had no significant difference in all groups and according to the physiological and biochemical indices, the appropriated salinity for juvenile chum salmon ranged from 10 to 20 during the catadromous migration.
