Reproductive cycle of the pearl oyster, Pinctada radiata (Mollusca: Pteridae), in the Zarat site (Gulf of Gabès, Tunisia)

Abstract

The gametogenic cycle of the pearl oyster, Pinctada radiata, from the Zarat region (Gulf of Gabes) in Tunisia was investigated monthly during a 1-year study of the reproductive cycle. Gametogenic activity was determined based on histological analysis of the gonads during the study period. P. radiata was found to have a clearly defined annual reproductive cycle, with two spawning periods per year. The first spawning period was observed in June and August for both sexes, and the second one was occurred from September to December for males and from September to November (except October) for females. The observed index shows that the main periods of gametogenesis and spawning around the year were from September to December for males and from September to November (except October) for female. Two types of hermaphroditism were observed following gonad ripening. The sex ratio showed a clear relationship with the size, with males the dominate sex among smaller individuals (shell height [SH] 65 mm). The condition index proved to be a strong indication of the gonad cycle as it illustrates the reserve accumulation during gametogenesis, maximum maturity and gamete emission. Maturity is roughly synchronous between sexes. The beginning of reproduction seems to be controlled by sea surface temperature rather than salinity.