Study On The Physiological And Biochemical Responses Of Apostichopus Japonicus To Environmental Hypoxia Stress

Apostichopus japonicus is also known as the sea cucumber,and belong to Apostichopus,Stichopodidae,Holothuroidea,Echinodermata. Apostichopus japonicus is typical temperate species. Sea cucumber culture is one of the important sunrise industries of northern China coastal aquaculture. In recent years,it’s scale is developing rapidly,and the culture become with local characteristics of northern farming industry and new ocean economic growth point. Dissolved oxygen, the oxygen content of the molecules in water, is a necessary condition for the survival of aquatic organisms. Dissolved oxygen is important parameters of biogenic element in water environment and it’s distributions and changes are affected by a variety of biological, physical and chemical factors such as photosynthesis, respiration, tide, temperature, salinity and circulation activities, biological activities and the impact of human activities. In addition, the summer is the critical period of sea cucumber culture management.The high temperature weather will caused a decrease in dissolved oxygen in the water, especially sea cucumber aquaculture in ponds can be reduced to about 2 mg/L, and it has a serious adverse effect on the normal physiological activity and growth of the sea cucumber, even lead to it massive diseases’ explosion or death.In this paper,we study that the oxygen consumption rate and ammonia excretion rate in the different dissolved oxygen levels and temperature level of sea cucumber with eight hours.We found that oxygen consumption rate and ammonia excretion rate were significantly decreased(P < 0.05) when dissolved oxygen of water below the sea cucumber’s critical point in different dissolved oxygen levels,and the oxygen consumption rate and ammonia excretion rate were no significantly difference(p﹥0.05) when dissolved oxygen higher than the sea cucumber’s critical point;In the different temperature level,as the temperature increased,the oxygen consumption rate increased significantly(p ﹤ 0.05) and ammonia excretion rate increased at first and then decreased,the ammonia excretion rate reached the maximum value in 16 degrees.The study showed that the changes of temperature and dissolved oxygen will cause the changes of sea cucumber oxygen consumption rate and ammonia excretion rate.In order to explore the response mechanism of hypoxia stress and provide guidance for culture under hypoxia condition, the effects of hypoxia stress on respiratory metabolism, energy metabolism and antioxidant capacity in Apostichopus japonicus were investigated. Experimental group were exposed to hypoxia(2±0.2 mg/L) 8 h, followed by reoxygenation(7±0.2 mg/L) 2.5 h, and tissues of muscle, respiratory tree and digestive tract in different times were collected. Content of physiological and biochemical parameters in different tissues and times were analyzed. The experimental results are as follows:The effects of hypoxia stress on respiratory metabolism in Apostichopus japonicus were investigated.With the duration of hypoxia exposure, activities of COX and SDH of the organization were significantly lower compared with the control group(p <0.05), and activities of LDH was higher(p <0.05) with the extension of hypoxic exposure time.The activities of COX、SDH and LDH of the organization returned to normal levels during reoxygenation.It indicated that the level of aerobic metabolism decreased while that of anaerobic metabolism and sugar fermentation reaction increased which could maintain provision of energy under hypoxia stress.The effects of hypoxia stress on energy metabolism in Apostichopus japonicus were investigated. With the duration of hypoxia exposure, activities of AK of the organization was significantly lower compared with the control group(p <0.05), and activities of lactic acid was higher(p <0.05) with the extension of hypoxic exposure time.The activities of AK and the content of lactic acid gradually returned to normal levels during reoxygenation.It indicated that the level of aerobic metabolism decreased,and it cannot produce enough energy to supply the body’s life,but also need to rely on anaerobic metabolism and arginine kinase produce ATP by catalyze the phosphoarginine.The effects of hypoxia stress on antioxidant ability in Apostichopus japonicus were investigated.With the duration of hypoxia exposure, activities of SOD of the organization was significantly lower compared with the control group(p <0.05), and activities of GST、CAT and T-AOC were higher(p <0.05) with the extension of hypoxic exposure time;the activities of MDA of muscle tissue was significantly lower compared with the activities of MDA of respiratory tree and digestive tract were higher.All of the oxidative stress parameters gradually returned to normal levels during reoxygenation.It indicated that hypoxia stress has an effect on the antioxidant defensive system,and lead to changes of antioxidant enzyme system.Hypoxia stress lead to great changes in the physiological and biochemical reaction of Apostichopus japonicus,and caused the level of aerobic metabolism decreased while that of anaerobic metabolism and sugar fermentation reaction increased.Facing hypoxia environment, in order to maintain the body’s normal activities, Apostichopus japonicus not only need to supply energy by aerobic metabolism and anaerobic metabolism,but also need to sugar fermentation reaction and phosphate reaction to produce energy. Perhaps this is a measures when the Apostichopus japonicus face hypoxia stress and it may also is a reason why Apostichopus japonicus are not resist to hypoxia.