抄録
Annual changes in oocyte development in the ovary and serum vitellogenin, an egg yolk precursor, were investigated in the rabbitfish, Siganus canaliculatus, in Okinawa, southern Japan. The progression of oocyte development was histologically divided into eight stages; the chromatin-nucleolus, perinucleolus, oil-droplet, primary yolk, secondary yolk, tertiary yolk, migratory nucleus and maturation stages. The oocytes laden with yolk first appeared in March. From April through June, the stage composition of oocytes was characterized by a high percentage of oocytes advanced beyond the primary yolk stage and was correlated with the increase of gonado-somatic index (GSI). Post-ovulatory follicles could be observed in the ovaries in May. The GSI values gradually decreased after June and were maintained at low levels from October through February. During these months, the ovaries were occupied by the immature oocytes at the chromatin-and peri-nucleolus stages. Vitellogenin, which was measured immunologically with rabbit anti-rabbitfish vitellogenin antiserum, changed in accordance well with the monthly fluctuation of GSI as well as development of oocytes laden with yolk. These results suggest that S. canaliculatus starts vitellogenesis in March and spawns several times in the following three months in Okinawa.
