Cultured pearls quality produced by the mollusk Pinctada margaritifera var. cumingi is determined by a panel of criteria, of which shape is one of the most relevant. Cultured pearls with round and semi-round (RS) shapes are the most valuable. Decreasing the proportion of other pearl shapes (OT: baroque, button, drop, oval), and especially the circled pearls (CL) and rejects (rebuts: RT), is an important challenge for the pearl industry. The present study examined the effect of grafter skill and season of graft on the variation in proportions of CL, RS, OT and RT cultured pearl shape categories in a mono-site culture (Mangareva island lagoon). Six large-scale grafting experiments, carried out in the same way as commercial grafting sessions, were made by seventeen experienced grafters over three seasons. After two years of culture, a total of 42,575 cultured pearls were harvested and sorted into shape categories. This study is the first to apply large-scale traceability to effects of individual grafter skill on cultured pearl shape in P. margaritifera. Grafter effects were clearly demonstrated on the proportions 1) of CL and RS, 2), to a in a lesser extent, of OT and RT, but 3) were low, affecting only a few percent of the overall means. For a high quality cultured pearl production, grafter effect could reduce CL rate by 7% and increase RS rate by 4%. In addition, the results indicate a significantly indirect influence of grafting season on shape class proportions, as these differ in autumn grafts, CL (−12%), RS (+13%) and OT (+24%), in comparison to winter and spring. Possible implications of "oyster" physiological reproductive status are discussed, as the difference in grafting season corresponds to differences in maturity of the recipient "oysters". Rates of RT were only increased (+14%) during the seasons when the lagoon water temperature was the coldest (winter) and the warmest (transition to summer).

International audienceSize is the most important and valuable quality of the cultured black-lip pearl, Pinctada margaritifera. As this pearl aquaculture is carried out at numerous grow-out sites, this study analyzes the environmental influence on pearl size parameters (nacre weight and thickness) in relation to the recipient oyster biometric parameters (shell thickness, height, width, and oyster weight) at harvest time. Toward this end, an experimental graft was designed by using a homogeneous donor oyster phenotype. The recipient oysters were randomly and equally transferred and reared in five commercial and contrasting grow-out locations. Overall inter-site comparisons revealed that the cultured pearl size (N = 2168) and the biometric parameters of the recipient oysters were highest for sites with warmer temperatures with low seasonal variation in comparison to the southern latitude sites. These results were supported by positive correlations between pearl nacre thickness and recipient oyster shell thickness, height, and width. In parallel, the biomineralization potential of the mantle graft was screened through four genes encoding aragonite (Pif 177, MSI60) and calcite (shematrin 9, aspein). As the gene expression levels were the same among all the donor oysters, this finding demonstrates that: 1) the pearl sac that originated from the mantle graft was not isolated from environmental variations during the culture period and 2) the phenotypic expressions of the two biomineralizing tissues in the recipient oyster were consistent (shell and pearl). In the near future, this knowledge will be helpful at the production sites of genetically selected donor oyster lines for growth produced in hatchery systems. Culture site dependence on pearl size realization in Pinctada margaritifera in relation to recipient oyster growth and mantle graft biomineralization gene expression using the same donor phenotype. Available from: https://www.researchgate.net/publication/299384948_Culture_site_dependence_on_pearl_size_realization_in_Pinctada_margaritifera_in_relation_to_recipient_oyster_growth_and_mantle_graft_biomineralization_gene_expression_using_the_same_donor_phenotype [accessed Oct 18 2017]

SummaryPinctada margaritifera is French Polynesia's most economically important aquaculture species. This pearl oyster has the specific ability to produce cultured pearls with a very wide range of colours, depending on the colour phenotypes of donor oysters used. Its aquaculture is still based on natural spat collection from wild stocks. We investigated three rare colour variants of P. margaritifera -orange flesh, and red and white shell colour phenotypes -in comparison with the wild-type black flesh and shell commonly found in this species. The study aimed to assess the geographic distribution and genetic basis of these colour variants. Colour frequencies were evaluated during transfer and graft processes of pearl oyster seed captured at collector stations. Among the collection locations studied, Mangareva Island showed the highest rate of the orange flesh phenotype, whereas Takaroa and Takume atolls had relatively high rates of red and white shell phenotypes respectively. Broodstocks were made of these rare colour variants, and crosses were performed to produce first-and secondgeneration progenies to investigate segregation. The results were consistent with Mendelian ratios and suggest a distinct model with no co-dominance: (i) a two-allele model for flesh trait, whereby the orange allele is recessive to the black fleshed type, and (ii) a three-allele model for shell trait, whereby the black wild-type allele is dominant to the red coloration, which is dominant to the white shell. Furthermore, the proposed model provides the basis for producing selected donor pearl oyster lines through hatchery propagation.

The black-lipped pearl oyster, Pinctada margaritifera, is the most important farmed mollusc species in French Polynesia. Donor oyster selection among wild P. margaritifera individuals, chosen according to their inner shell colour, makes it possible to obtain the broadest range of cultured pearl colours of any species. This study demonstrates the relative influence of using black [B] or red [R] outer shell phenotypes, combined with green [G] or yellow [Y] inner shell phenotypes, on pearl darkness level, colour categories and lustre. A large scale grafting experiment was designed and carried out over five grow-out locations, covering three archipelagos: Tuamotus, Society and Gambier. Results revealed that the [B + G] phenotypes may be used as donors to produce dark green pearl, which suit the demands of the Asian market; whereas, phenotypes incorporating [R] and/or [Y] phenotypes may be used to obtain multicolour pearls of medium/light darkness, which suit the demands of the European market. From an environmental point of view, the 1) [B] phenotype showed no significant variation for light and other pearl colour production, and 2) [Y] phenotype produced both the same rate of pearl darkness level and green colour pearls whatever the grow-out location. A classification tree model was built to predict, according to shell phenotype and culture location, the colour and darkness level of harvested pearls. Lustre was shown to be more influenced by the environment than by phenotype. These results should be taken into account in pearl farm production management and in selective breeding programmes.

In French Polynesia, the aquaculture of Pinctada margaritifera (Linnaeus, 1758) covers a large maritime exploitation area, spread over nearly 20 degrees latitude and longitude, with numerous pearl farms located in three archipelagos (Gambier, Society, and Tuamotu). As these archipelagos have specific seasonal temperature patterns each year, pearl oysters are subject to disparate and contrasting environmental regimes. This study aimed to examine the specificity of commercial pearl quality traits (n ¼ 2,236 samples) at the archipelago scale, in such a way as to provide preliminary data to design the most appropriate strategy for the distribution of hatchery-produced phenotypes. A large and standardized grafting experiment using the same donor phenotype was designed and carried out over six grow-out locations, covering the three archipelagos. Results revealed significant differences in commercial pearl quality traits among archipelagos, giving these groups of growing sites distinctive ''signatures'': (1) more color, less circles, and higher overall pearl grade in Gambier; (2) larger size with paler pearls in Tuamotu; and (3) darker pearls with intermediate size in Society. Characteristic differences in the environment and seasonal temperature ranges among the three archipelagos, corresponding to their distinct environmental conditions, can explain the specific variations between pearl quality traits among the sites. The strong disparities at archipelago scale should be taken into account in selective breeding programs for P. margaritifera so as to choose the most appropriate pearl oyster donor phenotype for use in each environment and thus enhance site-specific qualities for pearl production.