Dietary vitamin B₁₂ requirement and its effect on non-specific immunity and disease resistance in juvenile Chinese mitten crab Eriocheir sinensis

An 8-week feeding trial was conducted to investigate the optimum dietary vitamin B₁₂ requirement of juvenile Chinese mitten crab, Eriocheir sinensis, and its effect on non-specific immunity responses and resistance against Aeromonas hydrophila. Vitamin B₁₂ was supplemented to the basal diet at 0, 0.05, 0.1, 0.2, 0.4, 0.8 and 1.6mg/kg to formulate seven semi-purified diets. A diet free of vitamin B₁₂ and folic acid was also included as a control. Each diet was fed to E. sinensis (0.051±0.001g) in four replicates, followed by a challenge study for 2weeks. Relative growth rate and specific growth rate were best in crabs fed 0.2 and 0.4mgvitaminB₁₂/kg diets, followed by the 0.1, 0.8, 0, 0.05 and 1.6mg/kg groups and lowest in the control group (vitamin B₁₂ and folic acid free). Feed efficiency and survival rate peaked at the supplementation of 0.2mg/kg. The whole body crude protein of juvenile crabs was significantly higher when crabs fed 0.2-0.8mgvitaminB₁₂/kg than those fed the diets without vitamin B₁₂ supplementation. Total hemocyte count was significantly higher in crabs fed 0.2 and 0.4mgvitaminB₁₂/kg than those in the other feeding groups, and crabs fed the 0.2mg/kg diet had the highest phenoloxidase, lysozyme, acid phosphatase and alkaline phosphatase activities but the lowest cumulative mortality. Hepatopancreatic vitamin B₁₂ concentration increased as the level of vitamin B₁₂ supplementation increased. The optimum dietary vitamin B₁₂ requirement by E. sinensis is recommended at 0.20-0.22mg/kg diet.