Dietary mannan oligosaccharide (MOS) improves growth performance, antioxidant capacity, non-specific immunity and intestinal histology of juvenile Chinese mitten crabs (Eriocheir sinensis)

Mannan oligosaccharide (MOS) is a common prebiotics to improve health and immunity of animals in aquaculture. However, its optimum level and effects on the immune response in crab are currently unknown. The present study investigated the optimum level of dietary MOS supplementation and its effects on growth performance, antioxidant capacity, non-specific immunity and intestinal morphology of juvenile Chinese mitten crab (Eriocheir sinensis). Crab juveniles (2.95 ± 0.05 g) were fed either a control diet or one of the six diets supplemented with MOS (0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 0.6%) for eight weeks. The crabs fed 0.3% MOS showed greater weight gain, specific growth rate and lower feed conversion ratio than those fed the control diet. The acid phosphatase activity was significantly higher in the gut of crab fed 0.2% MOS than those fed the other diets except the 0.3% MOS diet. The lysozyme and alkaline phosphatase activities in the gut were higher in crabs fed the 0.1% and 0.3% MOS diets compared to those fed other diets. The antioxidant capacity was higher in crab fed the 0.2% and 0.3% MOS diets than those fed other diets. In addition, the mRNA expression of genes related to immunity (E. sinensis (Es)-Crustin, Es-Toll₂, Es-Lech and Es-prophenoloxidase (proPO)) in the hepatopancreas of crabs fed the 0.2 and 0.3% MOS diets were significantly up-regulated compared with those fed other diets. Duplicature length and width increased significantly in the crab fed 0.3% MOS than other diets. The optimum inclusion levels of MOS were 0.32%, 0.20% to 0.30% and 0.27% to 0.29% based on growth performance, antioxidant capacity and immunity, respectively. This study indicates that supplementing diets with MOS at 0.2% to 0.3% can improve growth performance and enhance antioxidant capacity and immunity in E. sinensis.