Effects of dietary Radix bupleuri root extract on the growth, muscle composition, histology, immune responses and microcystin-LR stress resistance of juvenile red claw crayfish (Cherax quadricarinatus)

The current study was conducted to determine the effects of dietary Radix bupleuri root extract (RBE) on the growth performance, muscle composition, immune responses, and microcystin-LR (MC-LR) stress resistance of juvenile red claw crayfish (Cherax quadricarinatus). Crayfish (0.28 +/- 0.02 g) were fed experimental diets con-taining graded RBE levels as 0 (Diet 1), 0.2 (Diet 2), 0.4 (Diet 3), 0.6 (Diet 4), 0.8 (Diet 5) and 1.6 (Diet 6) g/kg RBE for 8 weeks. The results showed that specific growth rate (SGR) and weight gain rate (WGR) were signif-icantly increased in the Diet 4 and Diet 5 groups. The content of muscle crude protein was significantly increased in the Diet 4 and Diet 5 groups, and the crude lipid content was significantly decreased in the Diet 5 group. Dietary RBE did not alter the structure of the hepatopancreas. Total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activities in hepatopancreas and plasma were significantly increased in Diet 4 and Diet 5 groups compared to the control group, while the malondialdehyde (MDA) content in hepatopancreas and plasma was significantly decreased in the Diet 5 group. Plasma alkaline phosphatase (AKP) activity was significantly higher in the Diet 3, Diet 4, Diet 5 and Diet 6 groups. Hepatopancreas and plasma PO activities were significantly increased in Diet 4 and Diet 5 groups. The mRNA levels of extracellular copper/zinc superoxide dismutase (ecCu, Zn-SOD), hemocyanin, C-type lysozyme (C-LZM), GPx, and selenium-dependent glutathione peroxidase (Se-GPx) were significantly up-regulated in the hepatopancreas of crayfish fed Diet 5 than those of the control group. After MC-LR challenge, the survival rates of crayfish in the Diet 4 and Diet 5 groups were significantly higher than the control group. The findings suggest that 0.6-0.8 g/kg of RBE can improve growth and muscle composition and enhance immunity and microcystin-LR resistance.