Effects of feeding different diets on survival, nutritional composition, digestion and immunity of juvenile Chinese mitten crab (Eriocheir sinensis) during overwintering

To study the effects of feeding different diets during overwintering on the survival, nutritional composition, digestion and immunity of Chinese mitten crab (Eriocheir sinensis), this experiment compared no feeding (NF group), feeding compound feed (CF group) and feeding chilled trash fish (CTF group) during overwintering on the survival rate, nutritional composition and the activities of digestive enzymes, antioxidant enzymes and immune enzymes of juvenile E. sinensis. The results showed that: ① After overwintering, the weight gain rate and hepatopancreas index of the CF group and CTF group were significantly higher than those of the NF group (P<0.05), but there was no significant difference in the survival rate among the three groups. ② After overwintering, the contents of fat and carbohydrates in the body and hepatopancreas of CF group and CTF group were significantly higher than those in NF group (P<0.05), and the carbohydrate content in the body and hepatopancreas of CF group was significantly higher than that in CTF group (P<0.05), while the water content of the hepatopancreas of the crab in the NF group was significantly higher than that in the CF and CTF groups (P<0.05). Regardless of feeding or not, the body protein content decreased significantly after overwintering, while the protein in the hepatopancreas increased significantly (P<0.05). ③ In regard to fatty acid composition, the contents of C18:2n6 (LA) in the body and hepatopancreas of the CF group were significantly higher than those in the NF group and CTF group, while the contents of C20:5n3 (EPA) and C22:6n3 (DHA) in the CTF group were significantly higher than those in NF group and CF group (P<0.05). ④ After overwintering, the activities of pepsin (pepsin) and α-amylase (α-AMS) in the CF group were significantly higher than those in the NF group and CTF group (P<0.05). ⑤ In terms of oxidative capacity, superoxide dismutase (SOD) activity in hepatopancreas and hemolymph in NF group was significantly higher than that in CF group and CTF group (P<0.05), total antioxidant capacity (T-AOC) activity in CF group was significantly higher than that in NF group and CTF group (P<0.05), and the content of malondialdehyde (MDA) in the hemolymph and hepatopancreas of female crab in CTF group was significantly higher than that in NF group and CF group (P<0.05). ⑥ As for the immunity of crabs, the activities of acid phosphatase (ACP) and alkaline phosphatase (AKP) in CF group were significantly higher than those in NF group (P<0.05). To sum up, E. sinensis should be fed with appropriate amount of diet during overwintering. The survival rate, hepatopancreas index, weight gain rate and nutrient accumulation of E. sinensis in the CF group were better than those in the CTF group. In addition, feeding compound feed is beneficial to the digestion of the E. sinensis, and enhances the anti-oxidation and immunity of E. sinensis. This study provides scientific reference and theoretical basis for rational use of overwintering diet for E. sinensis.