2022 Volume 34 Issue 3 Pages 59-69
The sea urchin Mesocentrotus nudus is a valuable commercial species in Hokkaido and northern Honshu, Japan, where artificial seeds produced in the hatcheries are released on fishery grounds for stock enhancement program. To develop a method for promoting broodstock maturation, we investigated the effects of photoperiod manipulation on the gonadal maturation of this species. Adult sea urchins were reared from December for 9-11 months under manipulated photoperiods where the annual change in day length between the two winter solstices was shortened to 6, 8, and 10 months, or advanced 2 months ahead of the natural photoperiod. Maturation progress was evaluated by observing the wet-squash gonad preparations and spawning reaction tests, which involved observing gamete release from the gonopore after removing the coelomic fluid. Experimental urchins reared under any of the accelerated and advanced photoperiods matured around August, one month earlier than those reared under the ambient photoperiod and the wild urchins collected from the coastal water. We conclude that the maturation of M. nudus can be promoted for early gamete collection in the hatcheries using the artificially accelerated or advanced photoperiods.
