Determination of Gender in the Pearl Oyster Pinctada margaritifera

The pearl industry in French Polynesia is based on exploitation of natural stocks of the blacklip pearl oyster (Pinctada margaritifera). It generates an annual turnover of €90 million. Improvements in pearl quality need genetic studies to improve the populations. This pearl oyster is a protandric species, in which the sex ratio normally is biased toward males. There is an increasing interest in gender control to find the mechanisms to augment female proportions for management purposes. This review summarizes information on exogenous and endogenous factors regulating gender in this and other bivalves, and concludes that P. margaritifera is a protandric hermaphrodite, developing as a male during the first 2 y, and without evidence of an effect from abiotic and biotic factors on gender during this phase. Later, pearl oysters progressively change to females, reaching a sex ratio close to 1:1 in specimens older than 8 y. At this stage, gender is apparently influenced by environmental parameters, but particularly by stress. Future research should seek to determine accurately the effect of temperature and food on sex ratios. Studies should be performed to characterize genes responsible for expression of gender. The use of hormones is a path that might be explored to influence the gender of pearl oysters.