INTRODUCTION
The Akoya pearl oyster, Pinctada imbricata (Röding 1798),has a broad global distribution and is found in temperate and tropical waters. This species has been farmed in Japan for over 100 yfor its small yet lustrous pearls. But Japanese production of high quality Akoya pearls has fallen from 118,000 kg in 1993 to 63,000 kg in 1996, with continuing production declines (Miyazaki et al.1999). This decline has in part been attributed to deteriorating water quality (Tomaru et al. 2001). It is well known that bivalve molluscs accumulate many pollutants within their tissue and shell,a fact that has led to their use as biomonitors of hydrocarbons (Sericano et al. 1995) and heavy metals (Bourgoin 1990, Phillips & Rainbow 1993) pollution in marine and estuarine waters. Pearl oysters are no exception to this, and have been used as biomonitors of heavy metals (Bou-Olayan et al. 1995) and hydrocarbons(Fowler et al. 1993). Whereas it is known that pearl oysters accumulate hydrocarbons and heavy metals in their tissues on exposure and that these compounds can exert toxic effects on other bivalve molluscs (Kennedy et al. 1996), there is little information regarding the tolerance of pearl oysters to pollutants.