1Mie Prefecture Fisheries Research Institute, Shima, Mie 517-0404, 2Graduate School of Bioresources, Mie University, Tsu, Mie 514-8507, Japan
We established a procedure that increased the production of high-quality pearls by keeping post-operative pearl oysters Pinctada fucata in low-salinity seawater. Oysters were implanted with a mantle graft and nucleus, and immersed in low (25 psu) or normal salinity (33 psu) seawater in tanks, or suspended from a raft in the sea for 14 days. Then, they were cultured in the sea by the ordinary procedure for several months until pearls were harvested. The harvested pearls were classified as nacreous, prismatic, organic or nucleus. Furthermore, nacreous pearls were classified as high or low quality, based on the proportion of blemishes. From the experiment, oysters immersed in 25 psu seawater showed the highest ratio of high-quality pearls, followed by those in 33 psu seawater. Another practical experiment with ten pearl farmers also showed that the ratio of high-quality pearls was significantly higher in 25 psu seawater than in the sea. These results indicated that the low-salinity treatment of oysters during the post-operative period could be an effective technique to increase the formation of high-quality pearls.