Effects of levamisole on the non-specific immune response and disease resistance of Chinese mitten crab Eriocheir sinensis

In order to determine the immunomodulatory effect of the dietary intake of levamisole in the Chinese mitten crab(Eriocheir sinensis),the crab were fed diets containing 0(control),100,200 and 300 mg levamisole kg~(-1) dry diet for 7 days.The total haemocyte count(THC),differential haemocyte count (DHC),phagocytic activity,respiratory burst(release of superoxide anion),phenoloxidase(PO)activity and lysozyme(LSZ)activity were examined at 0,2,4,6,and 8 weeks after administration of levamisole. Crab were challenged at 1.2×10~7 colony forming units(cfu) kg~(-1) crab weight with a virulent strain of Aeromonas hydrophila(CL99920) of E.sinensis at 4 weeks after administration of levamisole,and mortalities were recorded over a 10-day period.The results demonstrate that crab treated with levamisole showed significantly higher THC,the amount of hyaline cells(HC),phagocytic percentage(PP),respiratory burst (release of superoxide anion),PO activity and LSZ activity than those of the control group(P0.05).No significant differences in the amount of granular cells(GC)and phagocytic index(PI)of haemocyte among the crab fed with diets containing 0(control)and those fed with diets at 100,200 or 300 mg levamisole kg~(-1) dry die(P0.05).Furthermore,the levamisole treated E.sinensis were the more resistant.It was concluded that E.sinensis that were fed with diets at 100,200 or 300 mg levamisole kg~(-1) dry diet showed increased immune ability as well as resistance to A.hydrophila infection.Under the experimental conditions, the optimum dose of dietary intake of levamisole should be 200 nag levamisole kg~(-1) dry diet.