Effects of air exposure on survival, histological structure, non-specific immunity and gene expression of red claw crayfish (Cherax quadricarinatus)

Air exposure exerts unavoidable environmental stress during the transport of crayfish. This study evaluated survival, histological structure, non-specific immunity and gene expression in red claw crayfish (Cherax quadricarinatus) under air exposure. Survival experiment showed that crayfish under air exposure started dying after 24 h, and survival rate decreased to 62.2% and 20.0% after 36 h and 48 h respectively. In the second experiment, crayfish divided into six groups with different air exposure time (0 h, 4 h, 8 h, 12 h, 24 h and 36 h). Crayfish maintained in the normal culture environment were used as control (0 h), whereas other five groups were placed in tanks without water. Histopathological study found that air exposure resulted in swelling and vacuolation of hepatocytes and enterocytes. Total antioxidant capacity (T-AOC), activities of superoxide dismutase (SOD), glutathione peroxidase (GPx) and alkaline phosphatase (AKP) increased at 4–8 h short-term air exposure, and then decreased. T-AOC in hepatopancreas was suppressed significantly at 36 h exposure. Malondialdehyde (MDA) levels in both hepatopancreas and hemolymph raised after 4 h and then reduced to the initial level. Expression of antioxidant genes (SOD, GPx and Trx 1), immune-related genes (C-LZM, CRU-2, and SERPIN3), anti-stress related genes (HSP70 and HSP90) were induced after short-term air exposure, and then down-regulated. Expression of SERP, HSP21 and NFKBIA maintained high levels during 36 h air exposure, indicating that these genes play vital roles in the defense mechanism against air exposure. In brief, our study demonstrates that air exposure causes pathological changes in hepatopancreas and intestines, and altered antioxidant and immune status in C. quadricarinatus. The suppressed antioxidant status, leading to tissue oxidative damage, is one of the main reason for death of crayfish under long-term air exposure.