RELATIONSHIP BETWEEN DIET AND IMMUNE-RESPONSE IN ATLANTIC SALMON (SALMO-SALAR L) AFTER FEEDING VARIOUS LEVELS OF ASCORBIC-ACID AND OMEGA-3-FATTY-ACIDS

Juvenile Atlantic salmon (Salmo salar L.) were fed experimental diets containing megadoses of vitamin C1 and C2, respectively, and increasing amounts of omega-3 fatty acids for periods of 52 and 72 days. General resistance to infection was assessed after challenge with Vibrio salmonicida. Development of specific immune response after vaccination against Yersinia ruckeri was assessed as likelihood of survival after challenge and antibody level. Cell wall strength was assessed by the erythrocyte fragility test, and occurrence of morphological changes in various body organs was investigated. In the present study, no significant increase in general or specific resistance to infection was seen. Fish fed diets with megadoses of vitamin C2 had increased antibody levels and higher incidence of degenerative changes in skeletal muscle. Omega-3 fatty acids exerted an immunosuppressive action with both significantly lower likelihood of survival and lower antibody levels. An increased incidence of degenerative changes was also observed. On the other hand, increased levels of omega-3 fatty acids increased erythrocyte cell wall strength.