Histological Observations of Annual Reproductive Cycle and Tidal Spawning Rhythm in the Female Porcupine Fish Diodon holocanthus

抄録

Oocyte development was observed in the porcupine fish, Diodon holocanthus, to describe the annual reproductive cycle, and spawning with tidal rhythm, in Okinawa, southern Japan. On the basis of histological characteristics, the oocytes were divided into the following eight stages: the chromatinnucleolus, peri-nucleolus, yolk vesicle, primary yolk, secondary yolk, and tertiary yolk stages. Based on a monthly sampling the oocytes at the yolk vesicle stage first appeared in January. The oocytes laden with yolk were observed from April through June. After July, the ovaries were comprised of oocytes at the chromatin-nucleolus and peri-nucleolus stage. These results suggest that endogenous vitellogenesis in this species starts in January, and that exogenous vitellogenesis takes placefrom April through June. When the fish were collected according to the tidal phase (the spring and the neap tide) from May through August, the well-developed oocytes were observed with the spring tides from May through June. In contrast, the ovaries collected at the neap tide during the same periodcontained a small amount of the oocytes at the tertiary yolk stage and showed post-spawning features. Therefore, it is likely that D. holocanthus spawns between the spring and the neap tide.