Effects of dietary folic acid on growth, antioxidant capacity, non‐specific immune response and disease resistance of juvenile C hinese mitten crab E riocheir sinensis ( M ilne‐ E dwards, 1853)

An 8‐week study was conducted to determine folic acid requirement and its effect on antioxidant capacity and immunity in juvenile Chinese mitten crab E riocheir sinensis (Milne‐Edwards, 1853), followed by a challenge assay with the pathogen A eromonas hydrophila for 2 weeks. Folic acid was added to a basal diet at seven levels (0, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0 mg folic acid kg −1  diet), and a diet free of folic acid and vitamin B 12 was also included as a control. Crabs were fed twice daily in 32 tanks with 7.76–8.17 mg oxygen L −1 , 25.0–31.0 °C and 7.5–8.3 p H . Growth and feed efficiency were significantly greater in crabs fed ≥2.0 mg folic acid kg −1 , but not significantly different between crabs fed diets >2.0 mg folic acid. The superoxide dismutase activity and glutathione S‐transferase activity were highest in crabs fed ≥2.0 mg folic acid kg −1 , followed by those fed 0.5 and 1.0 mg folic acid kg −1 , and the control diet. The malondialdehyde content was highest in crabs fed the control diet, followed by those fed 0 mg folic acid kg −1 , and the lowest value occurred in those fed ≥0.5 mg folic acid kg −1 . Phenoloxidase activity and total haemocytes were significantly higher in crabs fed ≥2.0 mg folic acid kg −1 than other diets. Crabs fed 2.0 mg folic acid kg −1 had the highest lysozyme, acid phosphatase and alkaline phosphatase activities but the lowest cumulative mortality. The optimum dietary folic acid requirement by E . sinensis was estimated at 2.29–2.90 mg kg −1 diet.