Effects of air exposure time and temperature on physiological energetics and oxidative stress of winged pearl oyster (Pteria penguin)

The winged pearl oyster (Pteria penguin) is one of the most potential species used to produce large sized pearls. Waterless transport and nuclei implant process are two common handling practices for pearl oyster in aquaculture. These processes can cause air exposure stress. In order to investigate the physiological energetics and oxidative stress of pearl oysters exposed to air, live P. penguin were exposed to air for 6 h, 9 h and 12 h at different air temperatures (20 degrees C, 25 degrees C and 30 degrees C) before immediate re-immersing in seawater at 27 degrees C for their recovery. The air exposure time and temperature significantly affected the survival rates of P. penguin. Meanwhile, the optimum temperature was found to be 25 degrees C, in which the survival rate of P. penguin was> 90 % after 9 h of air exposure. In addition, five parameters of physiological energetics, such as clearance rate (CR), ingestion rate (IR), absorption efficiency (AE), respiration rate (RR), and ammonia excretion rate (AR) were significantly influenced by air exposure. When the duration of air exposure increased, simultaneous decrease in CR, IR and AE, and increase in RR and AR were observed. After re-immersing into seawater, these parameters of P. penguin exposed to less time (6 h or 9 h) and suitable temperature showed normal level after 96 h or less. Further, the air exposure influenced the activities of superoxide dismutase (SOD), catalase (CAT), total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) content in hepatopancreas and hemolymph. SOD activities increased after air exposure, and stabilized thereafter. After 6 h of air exposure, activities of CAT, T-AOC and GSH-Px rapidly increased, before gradually decreasing. There were no significant differences in the MDA content of hepatopancreas after 6 h and 9 h of air exposure, however, significant differences were observed after 12 h of air exposure. MDA contents in hemolymph showed significant increase after 9 h and 12 h of air exposure. In this study, it was demonstrated that the air exposure associated with common aquaculture practices strongly affected the physiological energetics and oxidative stress of P. penguin. This showed that excessive air exposure (unfavorable temperature and long duration) might lead to irreversible injures in P. penguin.