Effects of hypoxic stress on the digestion, energy metabolism, oxidative stress regulation, and immune function of the pearl oyster (Pinctada fucata martensii)

The activity of enzymes involved in digestion, energy metabolism, oxidative stress regulation, and immune function in the pearl oyster (Pinctada fucata martensii) was determined at 0, 0.5, 1, 2, 5, 10, 15, and 25 d following exposure to HG and NG to characterize the effects of hypoxia on pearl oysters. The protease activity was significantly higher in HG than in NG at 0.5 and 1 d but significantly lower in HG than in NG at 2, 5, 10, 15, and 25 d. The activity of amylase, lipase, and PK was significantly lower in HG than in NG at 0.5, 1, 2, 5, 10, 15, and 25 d. T-AOC and activity of CAT and LDH were significantly higher in HG than in NG at 0.5, 1, 2, and 5 d but significantly lower in HG than in NG at 10, 15, and 25 d. SOD and GPx activity was significantly higher in HG than in NG at 0.5, 1, 2, and 5 d and significantly lower in HG than in NG at 15 and 25 d. LPO content was significantly higher in HG than in NG at 0.5, 1, 2, 5, 10, 15, and 25 d. AKP activity was significantly lower in HG than in NG at 0.5, 1, 10, 15, and 25 d, but no differences in AKP activity were observed between HG and NG at 2 and 5 d. ACP activity was significantly higher in HG than in NG at 0.5 d and significantly lower in HG than in NG at 1, 2, 5, 10, 15, and 25 d. These changes in digestion, energy metabolism, antioxidant capacity, and immune defense promoted adaptation to early hypoxia. Long-term hypoxia decreased the survival rate of pearl oysters by decreasing involved in digestion, energy metabolism, immune responses, and oxidative stress regulation.