Effects of hypoxia on immune responses and carbohydrate metabolism in the Chinese mitten crab, Eriocheir sinensis

In aquaculture, hypoxia is an important stressor that can inhibit the healthy development of Chinese mitten crab, Eriocheir sinensis. The aim of this work was to research on how hypoxia (1 mg/L) followed by reoxygenation affects the immune response and carbohydrate metabolism in the Chinese mitten crab. The activities of immune-related enzymes including lysozyme (LZM), acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD) and phenoloxidase (PO) and concentration changes in haemolymph glucose, trehalose and hepatic glycogen were evaluated after 8 hr of hypoxia followed by 12 hr of reoxygenation. After 8 hr of hypoxia, the activities of LZM, PO, SOD and hepatic glycogen concentration significantly decreased to the minimum when compared to the control group, but the activities of ACP and AKP, and haemolymph glucose concentration significantly increased. After 12 hr of reoxygenation, the activities of LZM, ACP, AKP and SOD recovered to the normal level except SOD in plasma, while the PO, SOD in plasma and hepatic glycogen concentration were still significantly lower than the control level. No significant change was observed in trehalose concentration during hypoxia and reoxygenation periods. These results indicated that although the activities of ACP and AKP were likely increased to facilitate the hydrolysis of foreign matter, the overall strength of the immune response was decreased as LZM, PO and SOD activities were suppressed after exposure to hypoxic conditions. The energy stores of exposed crabs were reduced due to the expenditure of energy during exposure to hypoxic stress. In general, chronic hypoxia would impair the immunocompetence and increase the energy expenditure of Chinese mitten crab, further increased the risk of pathogen infection and feed coefficient, so the negative effects of hypoxia should not be ignored.