Shell colors and microstructures of four pearl oyster species in the South China Sea

Wild marine pearl oyster shells have rich colors, and the color and gloss of pearls cultivated by pearl oysters are closely related to the pearl layer color of the mantle. Therefore, in this study, four important wild marine pearl oyster species (Pinctada maxima, Pteria penguin, Pinctada margaritifera, and Pinctada fucata) were collected from the South China Sea, and a colorimeter was used to measure the color of their inner and outer shells. We analyzed the color range of their shells and the correlation between the color parameters; additionally, we observed the microstructure of their shells using a scanning electron microscope. The results showed that the color distribution and brightness of the inner shells of the four species were wider than that of the outer shells. In addition, the color distribution range of the outer and inner shells of the four pearl oyster species were P. fucata > P. margaritifera > P. maxima > Pt. penguin and Pt. penguin > P. fucata > P. margaritifera > P. maxima, respectively. Concerning the microstructures of the four pearl oysters, the shell structures of P. maxima, P. margaritifera and P. fucata had a honeycomb arrangement, whereas Pt. penguin had an irregular polygon structure. The P. maxima and P. margaritifera with a strong nacre secretion ability that area and thickness of the single crystal particles were larger than those of Pt. penguin and P. fucata.