Dietary intake of levamisole enhances the immune response and disease resistance of the marine teleost gilthead seabream (Sparus aurata L.)

In order to determine the immunomodulatory effect of the dietary intake of levamisole in the seawater teleost gilthead seabream (Sparus aurata L.), specimens were fed diets containing 0 (control), 125, 250 and 500 mg levamisole kg(-1) dry diet for 10 days. Growth, haematocrit, and phagocyte and lymphocyte responses were examined 0, 5 and 10 weeks after last administration of levamisole. The results demonstrate that 10 weeks after last administration of levamisole the specimens from the treated groups were larger and heavier than those of the control group. The experimental groups showed significantly lower haematocrit values 0 and 5 weeks after levamisole administration, although no differences were observed at 10 weeks. Leucocyte functions including phagocytosis and respiratory burst activity by phagocytes, and lymphokine (MAF) production by lymphocytes were enhanced by the dietary intake of levamisole. All of these responses peaked 5 weeks post-treatment. Serum complement activity was also found to be enhanced by treatment after 10 weeks. Fish fed 0 (control) and 500 mg levamisole kg(-1) dry diet were challenged with a virulent strain of Vibrio anguillarum 4 weeks post-treatment, and mortalities were recorded over a 30-day period. The levamisole-treated fish were the more resistant. The present results suggest that the introduction of levamisole into the diet of fish grown in farms could increase their resistance to infection, reduce fish mortality rates and offer economic benefits. (C) 1998 Academic Press Limited.