Abstract:Here we clarify the effects of gradually changing hypoxia and reoxygenation on respiratory metabolism and antioxidant capacity in Exopalaemon carinicauda. In the present study, we investigated oxygen consumption and reoxygenation in a respiratory chamber in which we first created a low-oxygen environment by preventing aeration and isolating the air, following which the chamber was aerated and reoxygenated. Continuously aerated groups were used as the control groups. Water and shrimp tissue samples were taken after 0, 1, 2, 4, 5 h of hypoxia and 1, 4, 8 h of reoxygenation from the beginning of the experiment. Further, we recorded the dissolved oxygen concentration of the water and the activities of the main respiratory metabolism enzyme and the antioxidant enzyme in shrimp tissues at different time points. The results indicated that over time, the dissolved oxygen concentration in the experimental group significantly decreased and was significantly lower than that in the control group (P<0.05). The dissolved oxygen concentration in the control group remained stable. After reoxygenation, the dissolved oxygen concentration in the experimental group quickly returned to the control level. Over time, cytochrome c oxidase (CCO) and succinate dehydrogenase (SDH) activities in the gill, hepatopancreas, and muscle tissue from the experimental group continuously decreased, lactic dehydrogenase (LDH) and fumaric reductase (FRD) activities continuously increased. In addition, the value of SDH/FRD showed a gradually decreasing trend. During reoxygenation, SDH, LDH, and FRD activities gradually returned to the levels of the control group in three organizations; CCO activity in muscle continuously increased but was significantly lower than that in the control group at 8 h (P<0.05). Furthermore, the value of SDH/FRD also showed a gradually increasing trend. Over time, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione s-transferase (GST) in the gill, hepatopancreas, and muscle tissue showed a trend of first increasing and then decreasing, but the activities of peroxidase (POD) continuously decreased in the hepatopancreas, while fluctuating in both, the gill and the muscle tissue. During reoxygenation, the activities of SOD and CAT in the gill, hepatopancreas, and muscle tissue all showed a trend of first increasing and then decreasing, but showed no significant difference with the control group at 8 h (P>0.05). With the increase of recovery time, the activities of GPX and GST in the three tissues returned to the level of the control group, but the activities of POD in gill and muscle tissue were significantly lower than those in the control group under reoxygenation at 8 h. The results show that with the continuous decrease in dissolved oxygen concentration, the aerobic metabolic level of E. carinicauda gradually decreased, and the anaerobic metabolic capacity gradually increased, while during reoxygenation, the aerobic metabolic capacity gradually recovered. Antioxidant enzymes such as SOD, CAT, POD, GPX, and GST may play an important role in responding to oxidative damage during hypoxia and reoxygenation.
