Dietary nano cerium oxide promotes growth, relieves ammonia nitrogen stress, and improves immunity in crab (Eriocheir sinensis)

Oxidative stress plays a crucial role in ammonia nitrogen toxicity. In this study, the beneficial effects of dietary nano cerium oxide (nano CeO 2 ) as a potent antioxidant were examined in the Chinese mitten crab ( Eriocheir sinensis ). Crabs were fed a diet supplemented with 0, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4, or 12.8 mg/kg nano CeO 2 for 60 d. The optimum supplementation level of nano CeO 2 that significantly increased weight gain rate and decreased feed coefficient was 0.8 mg/kg. This level also offered immune protection when crabs were kept under ammonia nitrogen stress and/or exposed to pathogen infection ( Aeromonas hydrophila ). Supplementation with 0.8 mg/kg of CeO 2 (i) relieved pathological damage to the hepatopancreas ; (ii) increased hemocyte counts, including total number of hemocytes, granulocytes , and hyalinocytes; (iii) decreased malondialdehyde content and increased antioxidant enzyme activities of superoxide dismutase and catalase in the hemolymph; (iv) increased the activities of lysozyme , acid phosphatase , and alkaline phosphatase in the hemolymph; and (v) increased gene and protein expression of cathepsin L in the hepatopancreas. Mortality increased when crabs were injected with bacteria under ammonia nitrogen stress, but dietary supplementation with 0.8 mg/kg nano CeO 2 decreased the mortality rate. Thus, the results of this study suggested that dietary supplementation with nano CeO 2 in crabs promoted growth and up-regulated immunity to bacterial infection under ammonia nitrogen stress.