Comparison Of The Quality Of Nucleated Pearls From The Mantle Of Hyriopsis Cumingii And Akoya Pearls And Their Correlation With Growth Traits

Nucleated pearls from the mantle of the freshwater mussel(Hyriopsis cumingii)are an emerging pearl cultivation technique with significant advantages such as high pearl quality and short nurturing cycle.It is widely known in the market as “freshwater Akoya” because of its resemblance to the Akoya pearls from the gonad of Japanese seawater mussel(Pinctada fucata martensii).In order to compare the quality of“freshwater Akoya” and Akoya pearls,to distinguish between the physical and chemical characteristics of them,and to further improve the quality of “freshwater Akoya” pearls,the following studies were carried out:1.Comparative identification of the quality and physicochemical characteristics of nucleated pearls from the mantle of H.cumingii and Akoya pearlsThis study was conducted to clarify the key physicochemical characteristics of nucleated pearls from the mantle of H.cumingii(freshwater Akoya)and Akoya pearls.Fourier transform infrared spectroscopy and ultraviolet-visible absorption spectroscopy were used for spectroscopic analysis.Optical microscopy and scanning electron microscopy were used for microstructural observation.ICP-MS was used for mineral element determination.The results showed that the infrared and ultraviolet-visible spectra of freshwater Akoya and Akoya pearls were generally similar,and both were composed mainly of aragonite.The surface of freshwater Akoya and Akoya pearls were characterized by a laminar growth structure and closely spaced contour lines,with the former having a scattered contour line arrangement and the latter having a consistent contour line arrangement.The cross-sectional structure of freshwater Akoya and Akoya pearls were similar and composed of aragonite plates.The concentrations of Mn,Zn,and Ba in freshwater Akoya were significantly higher than those of Akoya pearls(P <0.05),while the concentrations of Na,Mg,and Sr were significantly lower than those of Akoya pearls(P < 0.05).Na/Ca,Mn/Ca,Sr/Ca,and Ba/Ca did not intersect between freshwater Akoya and Akoya pearls,with Na/Ca having the lowest coefficient of variation(2.39%-6.25%),Sr/Ca having the second highest(6.98%-26.07%),and Mn/Ca and Ba/Ca had larger coefficients of variation(32.21%-264.58%).It is suggested that the quality of nucleated pearls from the mantle of H.cumingii is close to that of Akoya pearls,and the surface microstructure and Na and Sr concentration could be used as effective characteristics to distinguish freshwater Akoya from Akoya pearls.2.Correlation and path analysis of the quality of nucleated pearls from the mantle of H.cumingii with the growth traits of host musselsThis study was conducted to identify the growth traits related to the quality of nucleated pearls from the mantle of H.cumingii.Two-year-old H.cumingii were implanted with 10 nuclei of 5 mm size per mussel.These host mussels were cultured for 19 months to form commercial pearls.Correlation and path analysis of the key quantitative traits of pearls(pearl number/pearl formation percentage,maximum diameter,minimum diameter,roundness,nacre thickness),the growth traits of host mussels(shell length,shell width,shell height,body weight,shell weight,soft tissue weight),and nuclei(maximum diameter,minimum diameter,roundness)was investigated.The results showed that the average pearl formation percentage was(70±10.82)%,the average pearl size(minimum diameter)was 6.91±0.67 mm,and the average pearl roundness was(6.74±7.78)%.Pearl size and pearl nacre thickness were highly significantly and positively correlated with shell width,body weight,and shell weight(P < 0.01);and significantly and positively correlated with shell height and soft tissue weight of host mussels(P < 0.05).The correlation coefficient between shell width and pearl size and pearl nacre thickness was the highest,both being 0.688.The pearl formation percentage and pearl roundness were not correlated with any of the growth traits of host mussels(P > 0.05).The direct effect of shell width on pearl size and pearl nacre thickness(0.688)and the direct coefficient of determination(0.504)were the highest.These findings suggest that the shell width of the host mussels should be a key trait for cultivating of pearl size and pearl nacre thickness in nucleated pearls from the mantle of H.cumingii.