Family effect on cultured pearl quality in black-lipped pearl oysterPinctada margaritiferaand insights for genetic improvement

Abstract

-Individual Pinctada margaritifera molluscs were collected from the Takapoto atoll (Tuamotu Archipelago, French Polynesia) and used to produce ten first generation full-sib families in a hatchery system, following artificial breeding protocols. After three years of culture, these progenies were transferred to Rangiroa atoll (Tuamotu Archipelago, French Polynesia) and tested for their potential as graft donors. A large-scale grafting experiment of 1500 grafts was conducted, in which a single professional grafter used ten individual donor oysters from each of the ten families, grafting 15 recipient oysters from each donor. The recipient oysters were all obtained from wild spat collection in Ahe (Tuamotu Archipelago, French Polynesia). After 18 months of culture, 874 pearls were harvested. Highly significant donor family effects were found for nucleus retention, nacre thickness, nacre weight, pearl colour darkness and visually-perceived colour (bodycolor and overtone), pearl shape categories, surface defects and lustre, the last two of which are components of the Tahitian classification grade. No significant difference was recorded between the ten G1 families for the absence or presence of rings. The progenies could be ranked from "best" (i.e., the donor whose grafts produced the greatest number of grade A pearls) to the "worst". Some progenies had extreme characteristics: family B presented the greatest number of pearls with lustre (98%) and a high proportion of dark gray to black with green overtone pearls (70%). These results have important implications for the selective breeding of donor pearl oysters: it may be possible to reach a point where specific donor lines whose grafts produce pearls with specific quality traits could be identified and maintained as specific breeding lines.

Shell Growth Performance of Hatchery Produced Pinctada margaritifera: Family Effect and Relation with Cultured Pearl Weight

“…For example, Snow et al [37] hypothesized that pearls with a smooth surface and brilliant lustre are produced when consistent and regular crystal formation occurs, which is not compatible with a high nacre deposition rate. Ky et al [9] showed a strong family effect on pearl weight, but a significant effect of pearl colour was also detected, as well as a significant family * colour interaction. This indicates that potential relationships between weight and colour may vary among families.…”

“…Some keshi (small irregular shaped nacreous but non-nucleated pearls that form during the culture period after nuclei have been rejected) were also harvested, but not graded. Cultured pearls were then cleaned by ultrasonication in soapy water (hand washing) with a LEO 801 laboratory cleaner (2 L capacity, 80 W, 46 kHz) according to Ky et al [9]. Each pearl was mm) depends on pearl farming site as, in French Polynesia, the annual growth rate in shell size varies from 19.7 mm to 31.8 mm year -1 [23].…”

“…Shell and cultured pearl formation result from the bio-mineralization activities of two distinct tissues in a grafted pearl oyster: the mantle of the recipient oyster and the pearl sac built from graft tissues from the donor [5]. The pearl weight finally attained depends on several factors, including whether or not the donor oyster originated from the wild [8] or from a hatchery-produced family [9,10]. Some studies have shown phenotypic correlations between pearl weight and recipient oyster shell traits, e.g., for Pinctada fucata [11][12][13].…”

Influence of grafter skill and season on cultured pearl shape, circles and rejects in Pinctada margaritifera aquaculture in Mangareva lagoon

“…Biological mechanisms influencing rates of RS, CL, RT and OT (without circles) cultured pearl shapes are complex and only a few studies have focussed on the determining factors of these shapes in P. margaritifera. Using oysters produced in the hatchery system, Ky et al (2013) revealed that the presence of circled pearls was not influenced by donor family. In contrast, selection of donor oysters from the wild (Tayale et al, 2012) or produced in the hatchery (Ky et al, 2013) would be effective in increasing the proportion of round and semi-round pearls and decreasing the number of rejects.…”

“…Using oysters produced in the hatchery system, Ky et al (2013) revealed that the presence of circled pearls was not influenced by donor family. In contrast, selection of donor oysters from the wild (Tayale et al, 2012) or produced in the hatchery (Ky et al, 2013) would be effective in increasing the proportion of round and semi-round pearls and decreasing the number of rejects. A recent study revealed a significant phenotypic correlation between cultured pearl quality (grade) and shape in P. margaritifera (Ky et al, 2014b).…”