Accelerated photoperiod promotes gonadal maturation in the sea urchin Strongylocentrotus intermedius

In sea urchin hatcheries that produce seeds for the Strongylocentrotus intermedius stock enhancement program, promoting broodstock maturation is advantageous for early gamete collection and the resultant increase in seed size when they are released on fishery grounds. Here, the effects of photoperiod control were investigated to develop a method for promoting gonadal maturation. Adult sea urchins collected from the southwestern coast of Hokkaido in the Sea of Japan were reared from December to August or November under an ambient photoperiod and three accelerated photoperiods that shortened the annual change in day length between the two winter solstices to 8, 6, or 4 months. Maturation progress was evaluated by histological observations and spawning reaction tests, which involved observing gamete release from the gonopore after removing the coelomic fluid. The sea urchins reared under any of the accelerated photoperiods matured in June or July, 2-3 months earlier than those reared under the ambient photoperiod. The eggs and sperm collected from the photoperiod-treated sea urchins were fertilizable and grew normally into juveniles through metamorphosis. Therefore, accelerated photoperiods are effective for promoting maturation and early gamete collection in S. intermedius.