Examination of behavior, physiology and intestinal microbiological structure in small-sized sea cucumbers, Apostichopus japonicus: Relationship of color morph to seed quality

Seed selection is an essential process in the production of the sea cucumber, Apostichopus japonicus, as it is important to assure sufficient survival and growth, as well as production efficiency in subsequent aquaculture operations. It was considered that using morph color as an index for selecting high-quality seed would be valuable in this regard. The purpose of the present study was to evaluate the differences in body size, foraging behavior, melatonin levels, and intestinal flora structure of seeds of A. japonicus in dark and light color morphs. Here, we found that dark-colored seeds of sea cucumbers showed significantly longer foraging distances both in the day and at night, compared to the light-colored seeds. This indicates that dark-colored seeds of A. japonicus have a significantly greater locomotor ability. Melatonin levels of dark-colored seeds of sea cucumber were significantly higher than those of light-colored seeds, suggesting that dark-colored A. japonicus has greater antioxidant ability. In addition, in the composition of intestinal microbiota, the higher Firmicutes to Bacteroidetes ratio (F/B ratio) and a higher abundance of the phylum Planctomycetes were detected in dark-colored seeds of sea cucumber. Further, dark-colored seeds of sea cucumber had greater body weight/body length and body wall weight/body length, indicating that dark-colored seeds have a better growth potential. On the basis of the obtained results, it is suggested that aqua-culturists select dark-colored seeds in order to improve production efficiency. •Dark-colored seeds of sea cucumber have a significantly greater locomotor ability and higher melatonin levels.•The intestinal microbiological structure was different among sea cucumbers of different color morphs.•Dark-colored seeds of sea cucumber have significantly higher body index.•The present study establishes a new method for the early seed selection for A. japonicus aquaculture.