Reproductive cycles of Sebastes taczanowskii, compared with those of other rockfishes of the genus Sebastes

Abstract

Seasonal reproductive cycles were examined in both sexes of Sebastes taczanowskii,captured in southern Hokkaido, Japan. The reproductive cycle in females was divided into four periods: recovery (July—August), vitellogenesis (September-March), gestation (April—May) and parturition (June). Spermatozoa were first observed in November in the ovarian cavity, where no structural specialization was present for sperm storage. Fertilization of oocytes appeared to occur in April, when the oocytes underwent a rapid process of final maturation. Embryos developed in the ovary quite synchronously and were released in June; empty ovaries indicated the rockfish has a single parturition. The reproductive cycle in males comprised five periods: resting (December—July), early maturation (February—May), mid-maturation (June—August), late maturation (September—October) and functional maturation (November). In November when active spermatogenesis had been completed, a large amount of spermatozoa was preserved in the sperm duct, and the males were therefore ready for mating. A comparison was made of the reproductive cycles of four species of the genus Sebastes inhabiting southern and northern waters of Japan. It suggests that the northern species tend to prolong gametogenesis in both sexes while the southern species have the opposite tendency. Sperm storage in the ovary also tends to be longer in the northern than in the southern species.