Effect of Levamisole Supplemented Diet on European Sea Bass (Dicentrarchus labrax) Larvae in Respect to Survival, Growth Performance, Disease Resistance and Intestinal Histology

Information on the use of levamisole as feed additive in the production of marine fish larvae is scarce and no data is available for sea bass larvae. The current contribution highlights the effects of levamisole incorporation in sea bass larval diet on its survival rate, growth performance, proximate analysis, intestinal histology and disease resistance against the pathogenic Vibrio anguillarum. Larvae were assigned to four treatments (L0, L1, L2, L3) with different levels of levamisole (0, 100, 200 and 300 mg kg-1 diet), respectively. Fish were allocated into four triplicated groups of larvae per treatment. The diets were fed to sea bass post larvae (0.18±0.003 g) for 56 days. During the experimental period, no deaths were reported. Then, larvae were challenged with V. anguillarum, two weeks post-treatment. Results demonstrated a significant enhancement (P<0.05) in growth performance, feed efficiency, crude protein and lipid contents of larvae fed 200 mg kg-1 levamisole supplemented diet. The highest larval survival rate (80%) was also reported in L2 after V. anguillarum challenge. Histological sections of the intestinal tract in fish fed L2 demonstrated the greatest improvement in the length and width of the villi with the highest incidence of scattered goblet cells in the lamina propria and the most marked increase in the branching of mucosal folds and muscularis thickness than their corresponding in the other groups. Thus, the current results demonstrated that administration of 200 mg levamisole kg-¹ diet would be optimum for enhancing survival rate, growth performance, proximate analysis, improving the intestinal architecture, and immunity of sea bass larvae.