DIETARY-INTAKE OF LEVAMISOLE ENHANCES THE IMMUNE-RESPONSE AND DISEASERESISTANCE OF THE MARINE TELEOST GILTHEAD SEABREAM (SPARUS-AURATA L.)

In order to determine the immunomodulatory effect of the dietary intak e of levamisole in the seawater teleost gilthead seabream (Sparus aura ta L.), specimens were fed diets containing 0 (control), 125, 250 and 500 mg levamisole kg(-1) dry diet for 10 days. Growth, haematocrit, an d phagocyte and lymphocyte responses were examined 0, 5 and 10 weeks a fter last administration of levamisole. The results demonstrate that 1 0 weeks after last administration of levamisole the specimens from the treated groups were larger and heavier than those of the control grou p. The experimental groups showed significantly lower haematocrit valu es 0 and 5 weeks after levamisole administration, although no differen ces were observed at 10 weeks. Leucocyte functions including phagocyto sis and respiratory burst activity by phagocytes, and lymphokine (MAF) production by lymphocytes were enhanced by the dietary intake of leva misole. All of these responses peaked 5 weeks post-treatment. Serum co mplement 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 lev amisole-treated fish were the more resistant. The present results sugg est that the introduction of levamisole into the diet of fish grown in farms could increase their resistance to infection, reduce fish morta lity rates and offer economic benefits. (C) 1998 Academic Press Limite d.