Growth and physiological responses in the sea cucumber, Apostichopus japonicus Selenka: Aestivation and temperature

Aestivation is an adaptation of the sea cucumber Apostichopus japonicus Selenka to high temperature, however, the causations and physiological responses of aestivation are not well understood. This study deals with the relationship between temperature and aestivation. Sea cucumbers were allocated into four treatments. In two treatments of temperature elevation, the ambient temperature gradually was increased from 16 °C to 26 °C linearly (treatment FA) or by a fluctuating temperature profile (treatment FB). Two control treatments maintained constant temperatures of 16 °C and 26 °C, and were designated as optimum temperature of growth and threshold of aestivation, respectively. During the 40-day experiment, body weight, oxygen consumption, daily food intake, catalase (CAT) and superoxide dimutase (SOD) activities and heat shock protein 70 (Hsp70) levels were determined periodically. When the temperature gradually increased from 16 °C to 26 °C, the body weight of the tested sea cucumbers decreased gradually. After the ambient temperature reached 26 °C, the tested sea cucumbers in treatments of FA and FB were reared at 26 °C for an additional twenty days. During this period, symptoms of aestivation appeared in the tested sea cucumbers. Activities of antioxidases and Hsp70 levels increased when the ambient temperature increased from 16 °C to 26 °C, and decreased when the temperature was kept at 26 °C. These results indicate that aestivation in A. japonicus is an adaptive strategy to reduce the production of reactive oxygen species (ROS) and denatured proteins which were induced at high temperature.