An effective approach to improving fitness-related behavior and digestive ability of small sea cucumbers Apostichopus japonicus at high temperature: New insights into seed production

Abstract

Poor growth greatly reduces the production efficiency of small sea cucumbers Apostichopus japonicus in summer. The present study found that crawling frequency and tentacle activity frequency of sea cucumbers (~1 g of wet body weight) were significantly lower at 25 °C than those at 16 °C. These results suggest that high temperature greatly decreases fitness-related behavior of small A. japonicus. Stressed sea cucumbers (under air exposure for 1 h) showed significantly lower crawling frequency and tentacle activity frequency, compared to those not stressed at 25 °C. This indicates air exposure worsens the adverse effects on fitness-related behavior of small sea cucumbers at a high temperature. Tentacle activity frequency and crawling frequency of stressed A. japonicus cultured with artificial reefs were significantly higher than those cultured without reefs at 25 °C. This finding indicates that artificial reefs greatly improve the fitness-related behavior of stressed individuals at a high temperature. Survival rate, adhesion behavior, pepsin-like protease activity, defecation rate, and intestinal structure were significantly greater in sea cucumbers cultured with reefs than those cultured without reefs at 25 °C for 9 days. These novel results indicate that reefs greatly improve the digestive ability of sea cucumbers at a high temperature, which probably contribute to growth performances of sea cucumbers. The present study developed an effective approach to improving fitness-related behavior and digestive ability of small sea cucumbers, providing valuable insights into the seed production in summer.