Mantle regeneration in the pearl oysters Pinctada fucata and Pinctada margaritifera

Mantle tissue in pearl oysters (Pteriidae) is responsible for secreting the mother-of-pearl or nacre lining the shell. When grafted into another oyster, excised mantle tissue, commonly called 'saibo', is responsible for cultured pearl production. This study was undertaken to assess the process of mantle regeneration in the Akoya pearl oyster Pinctada fucata and the blacklip pearl oyster Pinctada margaritifera following mantle excision. Prior to saibo excision, oysters were anaesthetized with 2 mL L−1 propylene phenoxetol. Saibo tissue was excised from 50 P. fucata and 10 P. margaritifera. After excision, all oysters were returned to culture conditions. All oysters were maintained in panel (pocket) nets on a long-line at Magnetic Island, north Queensland, Australia. Oysters were anaesthetized and sacrificed 3, 6, 9, 12, 15, 20, 30, 45, 60 and 90 days after saibo excision to assess mantle regeneration using histological and histochemical techniques. Survival over the 90-day study was 100% and 70% for P. fucata and P. margaritifera, respectively. After excision, the mantle tissue healed within the first three days and began growing as connective tissue. Muscular development was seen between days 60 and 90 after excision. Shell formation abilities were recovered by day 15 when secretory cells and conchiolin secretions were first observed. Both P. fucata and P. margaritifera regenerated mantle to its original extent within the 90-day study. This is the first description of in vivo mantle regeneration in pearl oysters and the results have major implications for the lucrative cultured pearl industry. Our results indicate that mantle tissue donors need not be killed for pearl production. Those producing saibo that results in good quality pearls could be used as future parent-stock in breeding programs or for subsequent saibo donation and pearl production.