Reproductive biology of the pearl oyster, Pinctada radiata (Mollusca: Pteriidae), in northern Kerkennah Island (Gulf of Gabes)

Abstract

The reproductive cycle of the pearl oyster, Pinctada radiata, from Kerkennah Island (Gulf of Gabes) was investigated monthly between January and December 2007. Over the entire population, the sex ratio unbalanced, although males dominated among smaller individuals (shell height SH < 65 mm) and females were predominant in larger size-classes (SH > 65 mm). Evidence of protrandric hermaphroditism was observed with males maturing earlier than females. Males as small as 23 mm SL were found, whereas females were not observed at a size of less than 33 mm SL. The size at which 50% of the population reached maturity was 28 and 38 mm SL for males and females, respectively. Seasonal changes in macro- and microscopic properties of the gonads of both sexes showed that this species displayed a clearly defined annual reproductive cycle with a major peak in summer and a minor peak in autumn. The onset of reproduction appears to be triggered by the rising seawater temperature during spring and summer. P. radiata exhibited a short resting phase that occurred simultaneously in both sexes from the end of December until early February.