LIVER-GLYCOGEN, ENZYME-ACTIVITIES, AND PANCREATIC HORMONES IN JUVENILE ATLANTIC SALMON (SALMO-SALAR) DURING THEIR 1ST SUMMER IN SEAWATER

Our observation of very low liver glycogen concentration in 1-yr-old f eeding Atlantic salmon (Salmo salar) in seawater net-pens in Puget Sou nd, Washington, led to studies of their metabolic status. We assessed liver glycogen concentration, activities of some hepatic enzymes invol ved in glycogen synthesis, depletion, and gluconeogenesis, and plasma profiles of glucose and pancreatic hormones (insulin and glucagon) in yearling Atlantic salmon before and after seawater transfer. Liver gly cogen concentration in Atlantic salmon during the several months after seawater entry was much lower than in coho salmon (Oncorhynchus kisut ch) of the same age in seawater. Other metabolic and hormonal indices throughout the study did not differ substantially between the two spec ies. During their first summer in seawater netpens, seemingly healthy, feeding 1-yr-old Atlantic salmon smolts are prone to high mortality. We hypothesize that the virtual absence of glycogen reserves in the li ver makes seawater-adapted 1-yr-old Atlantic salmon juveniles particul arly susceptible to stress and may contribute to high summer mortality .