Effects of temperature and dissolved oxygen on the survival, activity and the adaptation strategy of metabolism in sea cucumber (Apostichopus japonicus)

Experimental ecological method was used to examine the changes in the distance moved per unit time and in the body surface area of the sea cucumber Apostichopus japonicus with a body weight of (39.35±0.40)g after they were shifted to an environment with a temperature of 15 °C and a DO concentration of 1 mg/L . The median lethal time (LT₅₀) of A. japonicus cucumber of two sizes large-size: with a body weight of (32.70±4.46) g; small-size: with a body weight of (10.31±2.03) g under hypoxia (1 mg/L) and three different temperatures (15 °C, 20 °C and 25 °C, with 15 °C as the optimum temperature) was also investigated. The diurnal metabolism in the A. japonicus of two sizes at different temperature (15 °C, 20 °C and 25 °C) and different DO levels 1, 3 and 6.5 mg/L (normoxia) were also investigated to evaluate the effect of temperature and dissolved oxygen on the survival, metabolism and athletic ability of A. japonicus. The results showed that first, when they were placed at a temperature of 15 °C and a DO concentration of 1 mg/L, the movement speed of A. japonicus was decreased gradually and finally all died at 72 h. The body surface area of A. japonicus increased first and then declined, and during the whole hypoxia period, the body of sea cucumber was elongated, higher than those in the control group. At the DO concentration of 1 mg/L, the LT₅₀ for the large and small-size A. japonicus was 54.0 h and 44.7 h, respectively, at the temperature of 15 °C, higher than those at the temperature of 20 °C (48.9 h and 39.3 h, respectively) and those at the temperature of 25 °C, (33.4 h and 28.9 h, respectively). The tolerance to low oxygen in the large-size A. japonicus was higher than the small-size one. Compared with those at the temperature of 20 °C and 25 °C, the two sizes of A. japonicus at the temperature of 15 °C were the most active at three DO levels. But compared with those at 15 °C and normoxia, the metabolic intensity of A. japonicus was also restrained at the DO concentration of 1 mg/L. Our analysis has shown that under hypoxia stress, A. japonicusmight employ some strategy such as elongating body to increase the body surface area to increase O₂ intake, decreasing movement speed and reducing metabolic intensity to cope with hypoxia and hence the survival time was prolonged.