Appropriate development of the pearl-sac in pearl oysters is an important factor influencing the quality of cultured pearls. In this study, a total of 110 black-lip pearl oysters (Pinctada margaritifera) with a mean (AE SE) antero-posterior measurement of 110.82 AE 0.41 mm and dorsoventral measurement of 112.06 AE 0.45 mm were grafted to allow histological examination and chronological description of pearl-sac development in this species. Beginning 2 days after grafting, oysters were sacrificed regularly until the 48th day and the pearl-sacs of sampled oysters were sectioned and examined. Graft tissue proliferated and developed into a complete pearl-sac within 14 days of grafting when the epithelial cells responsible for nacre secretion were fully developed. However, first nacre secretion onto the nucleus was not observed until 32 days after grafting. The presence and accumulation of haemocytes in the pearl pouch initially and in the pearl-sac thereafter is one of the primary factors potentially affecting pearl quality. Clumps of haemocytes present between the pearl-sac and nucleus caused distension of the pearl-sac from an ideally spherical shape. Furthermore, the presence of byssus in close proximity to the developing pearl-sac was demonstrated in this study. This has the potential to impact pearl-sac formation and resulting pearl quality. The findings reported in this paper provide a more detailed understanding of pearl-sac development in P. margaritifera and a basis for future research towards developing improved pearl culture practices and pearl quality.
The winged pearl oyster, Pteria penguin, is cultured primarily to produce half‐pearls (mabé). The mabé quality is influenced by culture techniques, but there is limited information in this field. P. penguin with mean (±SE) dorso‐ventral height of 250 ± 6.5 mm were used to investigate the influence of culture period and nucleus position on mabé quality. Oysters were relaxed using 1‐propylene phenoxetol, and five nuclei were glued at different positions to the inner surfaces of the oyster shells; three on the more concave left valve and two on the right valve. Nucleated oysters were then cultured for 10 months under commercial pearl farming conditions at Savusavu in Fiji. Nacre deposited at the base and top of the nuclei was measured monthly, from the 6th to the 10th months of culture and the different qualities of mabé produced at different positions were scrutinized. Nacre thicknesses at the base and top of the resulting mabé were significantly different at different months (P < 0.05) and the rate of nacre deposition was highest during the warmer months. The different positions of nuclei on the valve greatly affected the quality of mabé formed. After a 10‐month culture period, around 1 mm of nacre covered the nuclei although the best quality mabé were obtained after 9 months.
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