2.1 | Experimental animals
Adult A. japonicas (100±10 g) were collected in April 2018 from the coast of Weihai, Shandong, China. In order to reduce the effect of genetic variation, sea cucumbers were taken from the same aquacultural area, and the animals breeding were at the same time. The animals were acclimated in seawater at 15±1°C for 2 weeks prior to treatment and were fed a formulated diet once per day. After acclimation, evisceration was induced by injecting approximately 2 mL 0.35 M KCl into the coelomic cavity (Lina Sun et al., 2017; Lina Sun, Yang, Chen, Ma, & Lin, 2013). Eviscerated animals were kept in well-aerated indoor seawater tanks. We began recording observations at the point when the sea cucumber had expelled the entire intestine. The sea cucumbers have no feeding during intestine regeneration in our experiments.