Implanting Half-Pearl Nuclei in Different Positions in Mabe Pearls (Pteria penguin, Roding, 1798)

Abstract

A study was made comparing the success rate and nacre growth on half-pearl implantations in the Mabe pearl oyster (Pteria penguin, Roding, 1798). Implantations were made near the adductor muscle (#2), mantle edge (#3) and at an intermediate Position (#1). The rejection rate at Positions #1 and #2 (14.5 ± 4.9% and 14.0 ± 4.8% respectively), after 10 months were significantly lower (p < 0.05) than at Position #3 (19.0 ± 5.5%) (means ±95% conf. limits). The lowest mortality was found for oysters with an implant at Position #3 (26.0%) but this was also the position from which the oysters were most successful in rejecting the implant (19.0%). Oysters implanted at Positions #1 and #2 had higher final total mortalities that were not significantly different (35.0 ± 6.7% and 32.0 ± 6.5% respectively). Position #1 had the overall 10 month worst success rate (26.0 ± 6.1%), taking both rejection and mortality into account. About 15–20% of total losses were due to implantation failure and mortality in the first month: the average rate of loss of half-pearls was 3.33 ± 0.27% per month (n = 30). There is a trade-off between growth into larger half-pearls, overgrowth into heteromorphic pearls of no commercial value and relentlessly decreasing overall survival. A Profitability Index model shows that the best harvesting times are 8 to 10 months: losses of half-pearls offsets any gains from extra growth over this time. The Pearl farm was located in Sapum Bay, Muang, Phuket which is a well mixed bay on the east coast of Phuket island: the overall mean Secchi depth was 98.4 ± 2.8 cm, the air temperature was 28.3 ± 0.7 °C, the water temperature was 27.9 ± 0.9 °C and the salinity was 29.7 ± 0.2 ppt. Chlorophyll (Chl) content of the plankton (average total Chl a ≈ 2.23 ± 0.19 μg/l) tended to be higher during the Dry season (Dec–Mar) than in the Wet season (Apr–Nov) with no large changes in Chl ratios over the course of the study. One month had unusually high Chl values but this had no obvious effects on the oysters.