Xenografts and pearl production in two pearl oyster species, P. maxima and P. margaritifera: Effect on pearl quality and a key to understanding genetic contribution

Mantle xenografts between two Pinctada pearl oyster species, P. maxima (silver-lip pearl oyster) and P. margaritifera (black-lip pearl oyster), were used to examine their influence on pearl quality and to further our understanding of the respective contribution host and donor oysters have in pearl formation. Here, host oysters were implanted with mantle tissue originating from either the same species (allograft) or the other species (xenograft) and pearl formation allowed to proceed for 14 months, where after pearls were harvested and nuclei retention and pearl quality traits (nacre deposition/weight, shape, colour, complexion and lustre) recorded. Results showed that xenografts did not significantly affect pearl sac formation and subsequent nuclei retention (χ2 = 5.64, df = 3, P > 0.05), but did influence pearl colour, complexion, shape, nacre deposition and nacre weight (P < 0.05). Nacre deposition and weight were found to be higher in xenografts comprising of a P. maxima donor and P. margaritifera host, than in the reciprocal xenograft and allografts. Pearl colour and complexion were also strongly influenced by the donor oyster species used as xenografts, with P. maxima host oysters implanted with mantle from P. margaritifera producing generally black colour based pearls. Conversely, P. margaritifera hosts implanted with P. maxima mantle produced silver colour based pearls. This study demonstrates the potential of xenografts as a means to improve pearl quality traits such as pearl size, and highlights the role that donor oysters have in the realisation of pearl growth, colour and surface complexion.