USE OF MOIST DIETS FOR ATLANTIC SALMON (Salmo salar) WHEN TRANSITIONING FROM FRESH TO SEA WATER  

Atlantic salmon undergo a physiological transformation from being a freshwater fish to a salt water fish during spring approximately a year after hatching.    The biochemistry and physiology of the salmon are all altered so the fish will be able to survive in the ocean during adulthood.  During this transition the fish becomes fragile and mortality increases.  For salmon producers getting the fish through this period with the least mortality and keeping them on feed is important. In the northeast US and southeast Canada, soft feed or semi-moist feed has been used.  The purpose of this study is to determine if a new type of soft feed is able to get the salmon through this difficult period.  Atlantic salmon (initial weight ~55 g) were placed into a freshwater tank for three hours (to simulate transport of the fish to the net pen site) and the fish were stocked into tanks of seawater.  The fish were then fed one of four diets, two soft and two dry diets. There were not any significant differences between the individual diets except for feed efficiency.  The fish on the dry diets had significantly greater weight gain after 62 days and a higher feed efficiency.  The increased feed efficiency was due to the water content of the soft diet (~49% compared to 8% for the dry diets).  Survival and percent weight increase did not differ after 62 days.  After 70 days the fish on the soft feed diets  will be transferred back to dry feeds and the performance assessed for a further 28 days.