Effect of astragalus polysaccharides on nonspecific immunity of grass carp (Ctenopharyngodon idellus)

Abstract:

This experiment was conducted to investigate the effect of astragalus polysaccharides (APS) on nonspecific immunity of grass carp (Ctenopharyngodon idellus). 600 healthy grass carps were randomly divided into Group Ⅰ-Ⅳ, fed with the basal diet added with 0, 10.0, 30.0, 50.0 mg APS per kilogram body weight everyday respectively. Phagocytic percentage (PP), phagocytic index (PI) of leukocytes in blood and the activities of total superoxide dismutase (T-SOD), catalase (CAT) and lysozyme (LSZ) in serum were determined on D0, D8, D15, D22 and D29. On the 29th day of feeding, 20 grass carps of each group were infected by Aeromonas hydrophila and mortalities were recorded. The results indicated that APS added in diets can increase PP and PI of leukocytes, and enhance the activities of serum T-SOD, CAT, LSZ. The mortality rate of grass carps infected by A. hydrophila was significantly decreased when fed by APS (P<0.05) and the protective rate of Group Ⅱ-Ⅳ were 54.3%±6.4%, 52.9%±12.5% and 44.2%±4.8% respectively. It suggested that APS can enhance nonspecific immunity function of grass carp, and the effect of low dose was superior to high dose. The recommended dose of APS added to the diet applying in aquaculture was 10-30 mg/d per kilogram body weight.