In vitro induction of oocyte maturation in the Japanese sea cucumber Apostichopus japonicus by cubifrin and the developmental ability of the eggs

We describe the process of cubifrin-induced in vitro oocyte maturation in the Japanese sea cucumber Apostichopus japonicus, and we propose a procedure for practical hatchery application. Oocyte maturation occurred 40-50 min after stimulation of the ovaries by cubifrin. Concurrently, eggs were released from the ovarian tubules, initially by slow peristalsis, followed by active release after about 60 min. The first and second polar bodies were released from the eggs at 90-100 min and about 140 min, respectively. Cubifrin was more effective in inducing oocyte maturation at 1-100 nM than at 100 pM. Cubifrin at 1 pM-10 nM in rearing seawater had no effect on larval development. Delayed fertilization reduced the developmental ability of eggs. Broodstock could be maintained at 15-16 °C for up to about 50 days without affecting the developmental ability of eggs. Eggs matured in vitro and in vivo were similar in their developmental ability. In conclusion, the in vitro induction of oocyte maturation is effective in Japanese sea cucumber and represents a viable alternative to the induction of spawning by cubifrin injection.