Abstract:pH is an important environmental factor affecting the survival, growth, and immunity of aquatic animals. In general, alteration of environmental conditions often results in pH fluctuation in the aquaculture water of Apostichopus japonicus Selenka. However, little is known about the physiological response of sea cucumbers under pH stress. Therefore, the survival rate, growth, and antioxidant enzyme activities of sea cucumbers (7.02±0.81 g) were analyzed under different pH (control group, pH=8.4), low pH (pH 6.8, 7.0, 7.2, 7.4, 7.6, and 7.8), high pH (pH 8.6, 8.8, 9.0, 9.2, 9.4, and 9.6)) stress for 36 days. The survival rate of sea cucumbers decreased gradually with pH intension increasing and time extension, which in the groups ranging from pH 7.4 to pH 9.0 were 100%. There appeared to be a stress response and then death of individuals in the groups of pH 6.8, 7.0 and 9.6 from the third day, in which the whole group of sea cucumbers died after 30 days. Under different pH stress, the growth of the sea cucumbers differed significantly. The specific growth rate decreased with pH intension increasing and growth was negative growth in the group of pH 9.0. The superoxide dismutase (SOD) and catalase (CAT) activity of sea cucumbers among the pH treatment groups increased and was significantly higher than those of the control group, which increased at first and then decreased with pH intension increasing. The activity of SOD and CAT of sea cucumber in low pH groups increased to (74.92±2.24) U/ml and (14.99±2.38) U/ml peaking at pH 7.4, which was significantly higher than the control group. While in high pH groups, the activity of SOD and CAT of sea cucumber increased to (72.90±1.10) U/ml and (15.68±0.89) U/ml, peaking at pH 8.8 and pH 9.0 respectively. The results indicate that the pH range from 7.4 to 9.0 is appropriate for survival and growth of sea cucumbers, otherwise stress responses and even death of sea cucumbers are imminent.
