Abstract:Apostichopus japonicus that usually habits in the temperate zone, is one of the important aquaculture species at northern China coast. Dissolved oxygen, known as the oxygen content in water, is necessary for the survival of aquatic organisms and directly affects the enzyme activity, metabolism, and growth of aquatic organisms. Therefore, low dissolved oxygen during the hot weather is very harmful for sea cucumber aquaculture and has become an urgent issue. Here we investigated the effects of hypoxic stress on antioxidant capacity of A. japonicus. The experimental group was exposed to hypoxia [(2.0±0.2) mg/L] for 8 h, followed by reoxygenation [(7.0±0.2) mg/L] for 2.5 h. Then tissues from the muscle, respiratory tree, and digestive tract were collected at different time points. Levels of lactic acid, malondialdehyde (MDA), and activities of the antioxidant enzyme system in different tissues and time points were analyzed. It was found that during the exposure to hypoxia, the lactic acid content and activities of total antioxidant capacity (T-AOC), catalase (CAT) and glutathione-S-transferase (GST) were significantly higher compared with the control group (P<0.05), whereas the activity of superoxide dismutase (SOD) became lower (P<0.05) with the extension of hypoxic exposure. The level of MDA in the muscle tissue was significantly lower than in the control group (P<0.05), however, was higher in the respiratory tree and digestive tract. All of the oxidative stress indices gradually returned to normal levels during reoxygenation. These results indicated that as the aerobic metabolism was inhibited during hypoxia, the anaerobic metabolism was increased to maintain the energy supply. The elevated T-AOC, CAT and GST activities and declined SOD activity caused by hypoxia might be an antioxidant strategy to adapt to the hypoxic environment. Our study may provide useful information for the control of hypoxic conditions in sea cucumber aquaculture.
