Akoya pearl oysters (Pinctada fucata), into which a nucleus is implanted to produce spherical pearls, often show a low survival rate and a high rate of nucleus rejection. The hypothesis tested in this study is that using relaxing agents before implantation could reduce the oysters’ metabolism and improve graft success.

Tested Protocols

Researchers tested three relaxing agents: propylene phenoxetol, 30% magnesium sulfate, and 10% MS222. The optimal concentrations and durations were found to be 2.5 mL L⁻¹ for 6 minutes, 15 mL L⁻¹ for 11 minutes, and 2 mL L⁻¹ for 7 minutes, respectively.

At the beginning of anesthesia, oysters exhibited a high oxygen consumption, which gradually decreased and stabilized, unlike untreated oysters, whose metabolism remained more active.

Results on Survival and Rejection

Oysters transferred to the sea immediately after nucleation showed a higher survival rate eight months after the operation compared to those kept in concrete tanks for four weeks before being moved to the sea. The rate of graft rejection was also lower in the first group.

Impact on Pearl Quality

Despite these positive results on survival, pearl formation was better in oysters that had not received a relaxing treatment. The average pearl diameter in this group was 6.62 mm, compared to 6.52 mm (30% magnesium sulfate), 6.48 mm (propylene phenoxetol), and 6.46 mm (10% MS222) in treated oysters.

These results indicate that while the use of relaxing agents improves survival and reduces nucleus rejection, it may slightly affect the final size of the pearls produced.