The feces of sea urchins as food improves survival, growth, and resistance of small sea cucumbers Apostichopus japonicus in summer.

Mass mortality and low growth highly decrease the production efficiency and sustainable aquaculture development of the sea cucumber Apostichopus japonicus in summer. Sea urchin feces was proposed to address the summer problems. A laboratory study was conducted for ~ 5 weeks to investigate survival, food consumption, growth and resistance ability of A. japonicus cultured with the feces of sea urchins fed kelp (KF feces, group KF), the feces of sea urchins fed prepared feed (FF feces, group FF), and the prepared sea cucumber feed (group S) at high temperature (25 °C). The sea cucumbers of group KF had better survival (100%) than those of the group FF (~ 84%), higher CTmax (35.9 °C) than those of the group S (34.5 °C), and the lowest skin ulceration proportion (0%) when  they were exposed to an infectious solution among the three groups. These results suggest that the feces of sea urchins fed kelp is a promising diet for improving the survival and enhancing the resistance in A. japonicus aquaculture in summer. Sea cucumbers fed significantly less FF feces after 24 h of ageing than the fresh FF feces, suggesting this kind of feces became unsuitable for A. japonicus in a short time (within 48 h). However, the 24 h of ageing at 25 °C for the high fiber feces of sea urchins fed kelp had no significant effects on the fecal consumption of sea cucumbers. In the present study, both fecal diets provide better individual growth to sea cucumbers than the prepared feed. Yet, the feces of sea urchins fed kelp provided the highest weight gain rate (WGR) to sea cucumbers. Therefore, the feces of sea urchins fed kelp is a promising food to reduce the mortality, to address the problems of summer, and to achieve higher efficiency in A. japonicus aquaculture in summer.