SPAWNING PEAK OCCURS DURING WINTER IN THE JAPANESE SUBTROPICAL POPULATION OF THE PEARL OYSTER, PINCTADA-FUCATA-FUCATA (GOULD, 1850)

The pattern of gametogenesis in adult Pinctada fucata fucata from Zama mi Island, Okinawa Prefecture (26 degrees N), Japan, was examined and compared with to data reported for pearl oysters in other Indo-Pacific regions. Gametogenesis was observed in histological preparations of g onad from 232 adults sampled approximately monthly (1992-1993). Matura tion was observed throughout the year with a major peak in winter and a minor peak in summer. This is different from the restricted peak in summer reported for pearl oysters (P. fucata martensii) in the Japanes e northern temperate populations (33-34 degrees N). A difference in th e reproductive cycle between sexes was observed. After the peak of win ter spawning only the females entered a resting period during spring ( May). From summer to autumn there was a continuous occurrence of matur e individuals in both sexes which increased into winter. Differences i n reproductive periods among pearl oyster populations may prove useful for breeding programs in the pearl culture industry if environmental requirements for gonadal maturation are genetically influenced.