Effects of levamisole on the immune response and disease resistance of Clarias fuscus

Clarias fuscus were fed diets containing 0 (control), 75, 150, 300 and 600 mg levamisole kg(-1) dry diet for 7 days. Superoxide Dismutase (SOD), Maleic Dialdehyde (MAD), Myeloperoxidase (MPO), lysozyme and blood lymphocyte proliferation were examined at 0, 2, 4, 6, and 8 weeks after last administration of levamisole. Fish were challenged with Acinetobacter lwoffii 4 weeks post-treatment, and mortalities were recorded over a 40-day period. The results demonstrate that fish treated with levamisole showed significantly higher SOD activities, MPO activities, lysozyme levels, and lower MAD values than those of the control group (P < 0.05). No differences were observed on lymphocyte proliferation by intake of levamisole (P > 0.05). The levamisole-treated fish were the more resistant. 75 mg levamisole kg(-1) dry diet had no effects on the immune response of Clarias fuscus, whereas 600 mg levarnisole kg(-1) dry diet caused immunosuppression. The present results suggest that administration of 300 mg levamisole kg(-1) dry diet to Clarias fuscus should be optimum for stimulating nonspecific defence mechanisms and the specific immune response against Acinetobacter lwoffii. (C) 2005 Elsevier B.V. All rights reserved.