Effects of dietary beta-carotene on the immune response of rainbow trout Oncorhynchus mykiss

We attempt to assess the impact of different levels of dietary beta -carote ne on immune function in rainbow trout. Semi-purified diets containing 0, 4 0, 200, and 400 mg beta -carotene/kg dry diet were fed for 12 weeks to fish with average weight of 45 g. In addition to the humoral and cellular immun e parameters, growth and feed utilization were examined. There were no mark ed differences in growth and feed utilization showing that beta -carotene w as not particularly efficient in enhancing growth of rainbow trout. Of the immune parameters measured, total immunoglobulin was significantly highest for the 200 mg beta -carotene fed group. Serum complement activity (alterna te pathway) at 200 and 400 mg beta -carotene supplementation was significan tly higher than that of the unsupplemented group. An increasing trend in ly sozyme activity was observed, however, the differences among the groups wer e not significant. Phagocytic activity was similar among diet groups except at the highest level of supplementation where it was the maximum. Oxygen r adical production by peripheral blood leukocytes appeared to be lower at hi gher levels of carotenoid supplementation. Overall, dietary beta -carotene clearly enhanced immune response parameters in rainbow trout such as serum complement activity and total plasma immunoglobulin but did not show a defi nite influence for the other factors examined in the present study.