| The oyster. Pinctada fucata martensii Dunker. is the most important species for free seawater pearl production in China. It was reported that more than98%outputs of seawater pearls were produced by P. fucata martensii. Here, in order to discover the optimum production time of pearl, quality parameters of pearl produced from different months of nucleus insertion or pearl harvesting were compared each other. Besides, it was also analyzed for the relationship of phenotypic characters between the host oyster and pearl. The result showed that:1. According to the variation of water temperature of the mariculture area, nucleus insertion experiments were carried in February, March, April, May and July respectively. Pearls were harvested nearly at the same time, on December25to December27. It was showed that:(1). The average value of total weight, shell height, shell length, diagonal length of the host pearl oyster which insert nucleus in February (58.93±9.60g、70.18±5.18mm、66.07±5.73mm、62.51±5.64mm、57.02±4.39mm) were similar to these in March (56.07±9.84g、68.51±5.36mm.63.60±5.11mm、58.96±4.75mm、55.17±4.21mm). However, all these characters in both February and March were obvious less than that in either of May (64.43±11.57g、76.86±5.88mm、74.37±6.42mm、64.96±6.24mm、62.04±4.81mm) or July (64.21±11.67g、79.46±6.41mm、77.58±6.56mm、65.97±5.28mm、60.75±5.28mm)..(2). Either of the nacre thickness of pearl produced in March or July was0.35mm, significantly lowering than that in February(0.37±0.19mm), April(0.37±0.16mm) and May (0.41±0.17mm)(P<0.05). In addition, for pearl diameter and weight, there was no significantly difference among pearls produced in February (7.84±0.48mm,0.74±0.12g), April (7.85±0.40mm.0.74±0.11g), May (7.87±0.45mm,0.74±0.12g) and July (7.90±0.44mm,0.72±0.12g). However, there was significant difference for pearl diameter and weight between pearl produced in March (7.50±0.40mm,0.63±0.10g) and that in either other months (P<0.05).(3). There were significant positive correlation between either of pearl nacre thickness, pearl diameter, pearl weight and either of host oyster characters, including the shell wide, shell height, shell length, diagonal length, nacre thickness, total weight and total shell weight (.P=0.00). It was minimum for the correlation coefficient between shell wide and either of nacre thickness of pearl (0.164), pearl diameter (0.153) and pearl weight (0.202). On the contary, it is maximum for the correlation coefficient between the total shell weight and either of nacre thickness of pearl (0.382), pearl diameter (0.416) and pearl weight.(0.466). Moreover, there were significant negative correlation between either of pearl nacre thickness, the pearl weight and gradient of disease infection for shell (P=0.00). The correlation coefficient between gradient of disease infection and pearl nacre thickness was-0.13and-0.18for left and right shell respectively. The correlation coefficient between gradient of disease infection and the pearl weight was-0.117and-0.15for left and right shell respectively. Besides, there was negative correlation between gradient of disease infection and pearl diameter (P<0.05), with correlation coefficient of-0.096and-0.113for left and right shell respectively.2. The host oysters were divided into six groups according to age and size. Nucleus insertion experiment was carried in June. Pearls were harvested in September, November, January and March. The results showed that:(1). For every group, there was a increasing tendency from September to the next January, and a decreasing tendency since January for all characters, including shell length, shell high, total weight, total shell weight and left shell weight of the P. fucata martensii. Especially, there were significant differences for total shell weight and left shell weight of every group host oysters in January and March (P<0.05).(2). Thickness of nacre all groups increased about0.24mm in September. Since then, increasing speed of nacre slowed down gradually for groups of HY1-small, HY2-large, HY2-small and HY all decreased. Nevertheless, the increase speed of pearl nacre thickness showed a enhancing tendency for groups of SY.(3). The maximal values of lightness (L) were detected in January for nearly all groups but for HY1-lage and SY. For the groups of HY1-large and SY, the lightness value (L) reached the maximum of92.08±7.17and89.25±7.39in March, without significant difference compared with the lightness value on January (P>0.05).In a summary, this study results suggested that it is April and May that were the best time for nucleus inserting, while the periods from December to the next January were the best time for pearl harvesting. |
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