The effect of different culture methods on the quality of round pearls produced by the black-lip pearl oyster Pinctada margaritifera (Linnaeus, 1758)

Abstract

A range of culture units and husbandry methods may be used for pearl oysters and the two most commonly used for Pinctada margaritifera are panel nets and chaplets. In this study, six hundred P. margaritifera were grafted for the first time and cultured using panel nets or chaplets at three commercial farm sites to determine if these different culture methods influences resulting pearl quality. The pearls produced were compared in terms of size, shape, lustre, colour, surface perfection and overall quality. The highest proportion of pearls produced in all treatments was in the 10–11mm size category (37–54%) but culture method did not significantly (p=0.211) influence the size of pearls produced. Oysters held on chaplets produced more pearls with concentric surface grooves or ‘circles’ (47–60%) compared to oysters in held panel nets (43–45%) at all three culture sites. Oysters held in panel nets produced higher proportions of pearls in the more desirable ‘round’ and ‘semi-round’ shape categories (6% and 25%, respectively) than oysters held on chaplets (5% and 15%, respectively) at all three culture sites, and culture method had a significant impact (p=0.031) on pearl shape overall. Higher proportions of pearls in the ‘very high’ and ‘high’ lustre categories (8% and 40%, respectively) were produced by oysters held in panel nets compared to those on chaplets (3% and 16%, respectively) at each of the three culture sites. However, the overall impact of culture methods on pearl lustre was not significant (p=0.100). At all three culture sites, higher proportions of pearls assigned to grades ‘A’ (6%) and ‘B’ (46%) were produced by oysters in panel nets compared to those held on chaplets where 3% and 29% of pearls were assigned to grade ‘A’ and grade ‘B’, respectively. Oysters held on chaplets produced higher proportions of grade ‘C’ (49%) and grade ‘D’ (19%) pearls than those in panel nets (39% and 9%, respectively) at all three culture sites. The grades of pearls were significantly influenced (p=0.035) by culture method. This study clearly demonstrated the benefits of pearl production using panel nets compared to the traditional chaplet-based system used by the majority of pearl farmers in Fiji and throughout the Pacific. Pearls production using panel nets will provide better returns with higher profit margins for pearl farmers but requires greater outlay for infrastructure and labour that may be beyond the scope of most pearl farmers in Fiji and the Pacific. A detailed cost–benefit analysis of the two husbandry options would be beneficial to pearl farmers. Statement of relevanceThis paper presents novel new information showing that grafted P. margaritifera cultured using panel nets produced pearls with fewer ‘circles’ and of higher quality and value than oysters cultured using chaplets. The potential benefits to pearl farmers of pearl production using panel nets compared to the more traditional chaplet-based system are clear and the results of this study support improved pearl quality and income for pearl farmers in the Pacific.