To investigate the oxidative stress response of gill tissues and the energy metabolism of the adductor

muscle of Crassostrea angulata under hypoxic stress, six dissolved oxygen concentration gradients (0.5 mg/L,

1.0 mg/L, 1.5 mg/L, 2.0 mg/L, 3.0 mg/L, 4. 0 mg/L) were used to treat C. angulata under hypoxic stress for 96 h.

The total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity, catalase (CAT) activity,

malondialdehyde (MDA) content of C. angulata gill tissues, alkaline phosphatase (AKP) activity, lactate

dehydrogenase (LDH) activity, and glycogen content of the adductor muscle were determined using enzyme-linked

immunosorbent technique at the 6th, 12th, 24th, 48th, 72nd, and 96th hour of hypoxic stress. The results showed

that: (1) under low oxygen stress for 6–24 h, T-AOC, SOD activity, and MDA content showed the phenomenon of

first increasing and then decreasing, while CAT activity showed the phenomenon of first decreasing and then

increasing; at 24 h, the MDA content of the whole treatment group and the T-AOC activity and SOD activity of

part of the treatment group were restored to the level of the control group; and under hypoxic stress for 24–96 h,

T-AOC, SOD activity, and MDA content increased, then decreased, and then increased again, and CAT activity of

some treatment groups continued to decrease. T-AOC activity of all treatment groups and MDA content and CAT

activity of some treatment groups recovered to the level of the control group at 96 h, except for the 1.0 mg/L

concentration group, which did not have any significant difference from the control group. The SOD activity of the

rest of the treatment groups was significantly lower than that of the control group (P<0.05). (2) Over the 96 h of

hypoxic stress, LDH activity significantly varied among different treatment groups, with a total of three peaks

(P<0.05). AKP activity initially decreased and then increased with stress duration. Glycogen content decreased to

varying degrees with prolonged hypoxic stress time, and after 96 h, the 0.5 mg/L concentration group, showed a

significant decrease in glycogen content (P<0.05), while the other groups showed no significant differences from

the control group. These results suggest that C. angulata exhibits strong hypoxia tolerance by modulating changes

in various enzyme activities within the body to enhance the balance of body's oxidative stress response and energy

metabolism. However, extreme hypoxic environmental stresses still affect the physiological state of C. angulate.