Respiratory Metabolism and Antioxidant Response in Chinese Mitten Crab Eriocheir sinensis During Air Exposure and Subsequent Reimmersion

Chinese mitten crab, Eriocheir sinensis, often suffers from severe air exposure stress during transportation and culture; high mortality occurs due to desiccation. In this study, the effects of air exposure stress (0, 2, 4, 8, and 16 h) and reimmersion (2, 6, 12 h) on respiratory metabolism and antioxidant responses in Chinese mitten crabs were studied under laboratory conditions. The results showed that air exposure and reimmersion had a significant impact on the oxygen consumption rate (OCR), ammonia excretion rate (AER), oxygen to nitrogen ratio (O:N), superoxide dismutase (SOD), catalase (CAT), succinate dehydrogenase (SDH), and lactate dehydrogenase (LDH). Significant interaction between air exposure and reimmersion was observed for OCR, AER, O:N, SOD, CAT, SDH, and LDH in Chinese mitten crab. During the air exposure stage, SOD, CAT, and LDH activities in the gills and hepatopancreas first increased and then decreased as air exposure time increased. All of these parameters were significantly higher in the 4-h air exposure group than those in the control group. All the parameters were significantly lower in the 16-h air exposure group than those in the control group, except LDH in the hepatopancreas. However, SDH activity gradually decreased with increased air exposure time, and all the air exposure groups were markedly lower than those in the control group in the gills. During the reimmersion stage, OCR, AER, and O:N restored to normal levels after 12-h reimmersion, except in the 16-h air exposure group, where OCR and O:N were significantly higher than those in the control group and AER was significantly lower than that in the control group. The LDH activity in all groups restored to normal levels after 12-h reimmersion. The SDH, SOD, and CAT activities of the 2- and 4-h air-exposed groups returned to normal levels after 12-h reimmersion; however, these three parameters were still significantly higher in the 16-h air-exposed group than in the control group in the gills and hepatopancreas. Overall, Chinese mitten crabs reduce aerobic respiration and increase anaerobic respiration capacity during desiccation. Under air exposure stress, Chinese mitten crabs change their energy utilization mode to meet their energy demands and adjust their respiratory metabolism and antioxidant enzymes activities to adapt to adverse environments.