Reproductive cycle of a viviparous fish, the white-edged rockfish, Sebastes taczanowskii

Oogenesis and annual rhythm of oocyte development were observed histologically to clarify the reproductive cycle of a viviparous fish, Sebastes taczanowskii. The morphological changes in developing oocytes were described in seven stages. Major components of an oocyte were yolk globules and oil droplets, and development of yolk vesicles were invariably poor. Oocytes at the chromatin-nucleolus and peri-nucleolus stages were observed in the ovary throughout the year. Oocytes at the oil droplet and primary yolk stages first appeared in . July and September, respectively. During the long period of vitellogenesis from September to March, ovarian oocytes could be divided into two groups: the peri-nucleolus stage and the tertiary yolk or the more advanced stages. The stage composition in oocytes showed that type of oocyte development was group synchronous, and that these features were distinctly reflected in the mode of single brood production in the subsequent gestation. During the gestation period (April-May), all of the intra-ovarian embryos developed at the same rate, and GSI value became increasingly greater until just before parturition. Females released their brood all at once until the middle of June. Spent ovaries contained only oocytes at the chromatin-nucleolus and peri-nucleolus stages. From the results obtained, the annual reproductive cycle of S. taczanawskii was divided into four periods: the recovery period (JulyAugust), the vitellogenic period (September-March), the gestation period (April-May), and the parturition period (June).