DIETARY YEAST HYDROLYSATE ON GROWTH, DIGESTION, ANTIOXIDATION AND IMMUNITY OF RED SWAMP CRAYFISH (PROCAMBARUS CLARKII)

This experiment was conducted to investigate the effects of different levels of yeast hydrolysate (YHY) supplementation on growth performance, digestion, antioxidant and non-specific immunity of red swamp crayfish, Procambarus clarkii. A total of 300 crayfish with an average weight of (6.43±0.55) g were randomly divided into 5 groups (with 3 replicates in each group). These groups were fed with the basic diet supplemented with 0 (control group), 0.5%, 1%, 2% and 4% YHY, respectively. At the end of 8-week experiment, the growth performance, digestive enzyme activities of gastric tissue and hepatopancreas, antioxidant and immune capacities of hepatopancreas and serum biochemical indexes were determined. The results showed as follows: (1) YHY supplementation at levels ranging from 1% to 4% positively influenced the growth performance of P. clarkii. The 2% supplementation group exhibited peak values in survival rate (SR), final body weight (FBW), final body length (FBL) and hepatopancreatic index (HSI), being significantly higher than those in the control (P<0.05). The 1% supplementation group demonstrated the highest weight gain rate (WGR) and specific growth rate (SGR), which were significantly higher than those in other groups (P<0.05). (2) The crude protein (CP) content of whole body in 1.00% YHY supplementation group was significantly higher than that in any other group (P<0.05). The CP and crude lipid (CL) contents of muscle reached the maximum values in 2.00% supplementation group. (3) Gastric and hepatopancreatic digestive enzyme activities witnessed significant increases in groups supplemented with 2% to 4% YHY compared with the control (P<0.05). (4) The activities of antioxidant enzymes (catalase, CAT; total superoxide dismutase, T-SOD and total antioxidant capacity, T-AOC) and immune enzymes (alkaline phosphatase, AKP and acid phosphatase, ACP) in hepatopancreas reached their maximum values in the 2% YHY supplementation group, the malondialdehyde (MDA) content reached the minimum value concurrently, and there were significant differences compared with the control group (P<0.05). (5) Serum total protein (TP) and albumin (ALB) contents were notably higher in 2% YHY supplementation group compared to other groups (P<0.05). The activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were significantly lower in 1% and 2% supplementation groups relative to other groups (P<0.05). The results showed that 2% dietary yeast hydrolysate could significantly enhance the digestion, growth performance and muscle’s CP and CL contents, as well as significantly improve the antioxidant capacity and non-specific immunity of P. clarkii.