Fat dynamics of Atlantic salmon Salmo salar L. smolt during early seawater growth

摘要

Growth of Atlantic salmon Salmo salar L. smolt is poor in the period immediately following transfer to seawater, and the fish may use endogenous reserves to meet metabolic requirements at this time. Fat dynamics of smolt that differed in 'fat status' (10-12 versus 5-7% body fat) at the time of transfer to seawater were examined in fish fed either high-(31% fat, 41% protein) or low-fat (18% fat, 49% protein) feeds during seawater rearing. Samples were taken at intervals over 14 weeks to monitor changes in fat of the fillet, viscera and remaining carcass (head, skeleton, skin and 'belly flap'). Growth rates (SGRs) were low during the first 3-6 weeks, but improved with time and SGRs for the 14 weeks were approximately 1% d(-1) . Fat status of the smolt appeared to influence growth in seawater, because the fish that had been held on the high-fat feed in fresh water grew less well than those given low-fat feed at that time. At transfer to seawater, the fillet housed 20-25% of the body fat, and the carcass over 50%. After 14 weeks, the fillet held 32-35% of the body fat, and viscera 19-26%, but the carcass, with 40-49%, was still the major fat depot irrespective of dietary treatment. Thus, the carcass is a major fat storage depot in Atlantic salmon smolt, but the fillet appears to become more important as the fish increase in size.