EFFECTS OF ALPHA-TOCOPHEROL AND DIETARY OXIDIZED FISH-OIL ON THE IMMUNE-RESPONSE OF SEA BASS DICENTRARCHUS-LABRAX

Sea bass weighing about 35 g were reared on 6 experimental diets differing in the level of alpha-tocopherol (vitamin E) supplementation (0, 40 or 300 mg kg 1) and fish oil quality (fresh or oxidized). After 35 wk, group comparisons of haematological parameters were made and alpha-tocopherol levels in anterior kidney, spleen, and thymus were assessed in pooled samples. Non-specific immune factors assayed were: (1) plasma lysozyme and complement activities, (2) natural haemolysis of sheep red blood cells (SRBC), and (3) chemiluminescence (CL) response of head kidney phagocytes. Humoral antibody production was also assessed for each group after immunisation with Vibrio anguillarum 408. Resistance to bacterial infection was assessed comparatively according to diet. The levels of alphatocopherol in the different tissues were a function of the dietary vitamin E concentrations and were lower when oxidized fish oil was added to the diet. Erythrocyte fragility was raised in vitamin E depleted groups as well as in fish fed diets containing oxidized oil. Disease resistance, antibody response to V. anguillarum antigen, and haemolytic activity of sera were not affected by dietary treatment. Plasma lysozyme activity was lower in groups fed diets containing oxidized oil or not supplemented with vitamin E, and complement activity was higher in the fish that were fed the diet containing fresh oil and 300 mg vitamin E kg-1. One month after vaccination, the CL peak response of head kidney phagocytes, stimulated by opsonized zymosan, was significantly lower in the fish that were fed the diet containing oxidized oil and not supplemented with vitamin E.