Effect of gender on Akoya pearl quality

doi:10.1016/j.aquaculture.2014.12.028

Aquaculture

Volume 437, 1 February 2015, Pages 333-338

https://doi.org/10.1016/j.aquaculture.2014.12.028 Get rights and content

Highlights

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The proportion of low-quality pearls was observed to be lower from male oysters than from female oysters.
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The optical characteristics of each pearl were determined according to the sex of the recipient Akoya pearl oyster.
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The sex of the Akoya pearl oysters affects not only the quality of pearls, but also nacre growth.
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Nacre growth in female pearl oysters is related to ovarian development.

Abstract

During the cultivation of pearls, a mantle piece and pearl nucleus are transplanted into a recipient Akoya pearl oyster (Pinctada fucata). The gonad has been the area of transplantation since pearl culture techniques were originally developed. Transplantation into gonads without germ cells is vital for the production of high-quality pearls. Almost all pearl cultivators thus perform forced elimination of the germ cells from the gonads before transplantation. However, little attention has been paid to the sex of the pearl oyster, even though the gonad state is vital for the production of high-quality pearls. In our present study, we investigated the relationship between the sex of the recipient Akoya pearl oyster and pearl quality. We found that the rate of production of commercially valuable pearls was higher for male than for female recipient oysters. Furthermore, the nacre in male recipient oysters grew evenly every month whereas it was added less uniformly in female recipient oysters. Nacre growth in female pearl oysters was found to be related to ovarian development. These results indicate that differences exist in the pearl formation ability of male and female Akoya pearl oysters. By understanding the relationship between the sex of Akoya pearl oysters and pearl quality, high-quality pearls could be cultivated with better efficiency.

Introduction

The characteristics of cultured pearls are influenced by the two types of oysters used in this process: the donor, which provides a small piece of mantle to be transplanted, and the recipient, which receives the pearl nucleus and a small piece of mantle (Southgate and Lucas, 2008, Wada, 1999). Generally, the brightness, luster, and color of cultivated pearls are affected by the donor oyster, whereas the thickness of the nacre is affected by the recipient oyster (Wada and Komaru, 1996). The pearl nucleus and the piece of mantle are transplanted into the gonads of the recipient pearl oyster.

Pearl culture efficiency is affected by the state of the gonads, particularly that of the germ cell, and the sperm and egg in the gonads have been directly linked to the quality and efficiency of the pearls produced in this way (Wada, 1991). Nonetheless, it is unclear what effects gonads have on pearl formation. For these reasons, pearl farmers are forced to eliminate the germ cells from the gonads of pearl oysters prior to transplantation. In general, two methods have been used to achieve this: in one method, Akoya pearl oysters are cultured in narrow cages before the spawning season to suppress gonadal development; in the other method, Akoya pearl oysters are moved to a warmer sea area or treated with ozonated seawater to stimulate spermination and ovulation during the prespawning season. However, both of these methods are expensive and time consuming. Moreover, the Akoya pearl oyster is weakened by these treatments. For the pearl farmer, gonad management in the pearl oysters strongly impacts the quality and efficiency of pearl production, but the relationship between the pearl and gonad is still poorly understood. In our present study, we have analyzed the effect of Akoya pearl oyster sex on pearl production to better understand the relationship between pearl cultivation and oyster gonads.

Section snippets

Relationship between sex and pearl yield rate

To examine the relationship between the sex of the pearl oyster and pearl yield in culture, we assessed sex and pearl quality in individually cultured pearl oysters harvested from different pearl farms. To reduce the likely impact of data variation and complexity on result interpretation, we selected farms which utilize the single nucleus transplantation method and Akoya pearl oysters of Chinese and Japanese (for host oysters) origin. The practices used on each included farm are described in

Cultured pearl quality from male and female Akoya pearl oysters

We investigated pearl quality from eight oyster farms (Fig. 1A), among which differences in the rate of low-quality pearl production were evident. Interestingly, the proportion of low-quality pearls was observed to be lower from male oysters (30.8% on average compared with 47.7% in females). Thus, cultured pearl quality appeared to be clearly affected by the sex of the recipient Akoya pearl oyster.

Characteristics of the pearls cultivated from male and female Akoya pearl oysters

To examine the relationship between pearl quality and sex in more detail, the sex of the recipient

Discussion

To produce higher quality cultured pearls, various factors must be taken into account, such as the condition of the Akoya pearl oyster, the condition of the sea, and the transplantation technique (involving a pearl nucleus and a small piece of mantle). In particular, the state of the gonad of the recipient pearl oyster is crucial to the production of high-quality pearls (Wada, 1991). Accordingly, pearl farmers have expended a great deal of expense and time to optimize the gonadal state of their

Acknowledgments

This study was supported by a Grant-in-Aid from the Science and technology research promotion program for agriculture, forestry, fisheries and food industry (26019A).

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Transcriptome and proteome analysis of Pinctada margaritifera calcifying mantle and shell: focus on biomineralization
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Evaluating and identifying pearls and their nuclei by using optical coherence tomography
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There are more references available in the full text version of this article.

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The influence of donor and recipient oyster red and blue shell nacre interference color on Pinctada fucata martensii pearl quality
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The influence of shell body color on pearls has been studied extensively, but the effect of shell interference color selection on pearls has not been fully understood yet. Because interference color is an important factor determining pearl quality, it is important to study whether the shell interference color of the donor and recipient oysters has any influence on the resulting pearls' interference color to cope with the market demands. We report that selective breeding of red- and blue-line Pinctada fucata martensii pearl oysters produce high-quality pearls based on shape, flaw, color, size, and luster assessment categories. Saibo from red- and blue-line donors was implanted with a rounded nucleus into the red- and blue-line recipient oysters from the same batch in four treatments which we refer to as DRMR (red-donor, red-recipient), DRMB (red-donor, blue-recipient), DBMR (blue-donor, red-recipient), and DBMB (blue-donor, blue-recipient) oysters. Pearl shape and flaws, body yellowness index (YI) and interference value color categories, luster value, total nacre and tablet thickness, and surface microstructure for these treatments are reported. More DRMR pearls are high grade (H) than DBMB, DBMR, and DRMB pearls. Using electronic pearl quality measuring devices, DRMR pearls have the lowest YI and highest interference color values, rendering them superior in color category. Whole nacre thickness of pearls estimated by the SEM on the pearl section reveal DRMR pearls have significantly (p < .001) thicker nacre than DBMB, DBMR, and DRMB pearls, rendering them generally larger in size. DRMR pearls also have significantly (p < .001) thicker nacre tablets in basal, middle, and surface regions of the nacre layer. Whereas luster does not differ significantly among treatments (p > .05), DRMR pearls are superior to those of other treatments in their shape, reduced number of flaws, color, and size. We consider that P. fucata martensii oysters with red shell nacre interference color improve pearl quality, and for the purposes of pearl culture should be selected for. These results are of commercial importance, especially where P. fucata is cultured for pearl production.
The effects of nacre microstructure on green and pink interference colors in Pinctada fucata martensii pearls
2021, Aquaculture
Citation Excerpt :
Results of this present study might benefit the pearl industry, particularly where P. fucata is cultured. We progress what is known of Akoya pearl oyster culture, nacre biomineralization, and its relationship with pearl quality (Atsumi et al., 2018; Muhammad et al., 2020, 2017; Sato et al., 2013; Sato and Komaru, 2019), and complement research of others who have studied similar topics (Iwai et al., 2015; Odawara et al., 2017). Further study on pearl nacre microstructure with specific interference colors will assist in understanding how interference colors might affect pearl quality, to improve pearl quality output to meet market demand.
Despite the importance of both pearl body and interference colors in determining pearl quality, only body color has been studied extensively. We report novel information on relationships between pearl nacre microstructure and interference color saturation and hue in pearls produced by Pinctada fucata martensii. The interference color saturation and hue of 60 round pearls was subjectively graded by eye by an expert. Nacre optical characteristics and microstructure of pearls of 1) high (grade A) and low (grade B) interference color saturation, and 2) pink and green interference hues are reported. Using electronic pearl quality measuring devices, grade A pearls have higher interference color values (0.050 ± 0.061) than grade B pearls (0.008 ± 0.039), consistent with subjective grading by eye. SEMs of surface microstructure reveal the nacre tablet area of grade A pearls, 4.079 ± 2.173 μm², to be generally greater than that of grade B pearls, 2.940 ± 1.213 μm² (P < .001), with the nacre surface of grade A pearls smoother than grade B pearls. Regardless of grade, the basal and middle regions of the nacreous layer of pearls with a pink interference color hue differ significantly in nacre tablet thickness (p < .001), but nacre tablet thickness does not differ significantly between their central and surface regions. The nacre tablet thickness of pearls with green interference color hue changes more consistently from the basal to surface regions, with only the basal and surface regions differing significantly in thickness (p < .001). We report pearl interference color to be greatly affected by nacre tablet microstructure. The saturation of pearl interference color is affected by the smoothness of the nacre surface, which is a function of the surface nacre tablet area. The hue of pearl interference color is affected by differing thicknesses of nacre tablets through the nacreous layer, from surficial to basal regions. Results of this study might benefit the pearl industry, particularly where P. fucata is cultured. Additional study on how shell matrix protein genes are related to nacre tablet biomineralization would improve understanding of the mechanisms affecting pearl nacre microstructure, leading to saturation and hue of pearl interference colors.
Sex determination in pearl oyster: A mini review
2019, Aquaculture Reports
Citation Excerpt :
In pearl oysters, the gonad is a vital organ due to its involvement in the pearl production process. During nucleus insertion, the nucleus is inserted into the gonad and mostly gonads without gamete are favorable (Iwai et al., 2015). However, the total elimination of the gamete has also been reported to suppress the physiology and metabolic rate of pearl oysters which intend reduce pearl productivity and quality.
Pearl aquaculture is an intensive pearl production method which has gained much interest over the years with pearl oysters been the main organism involved in the production of sea pearls. This has attracted growth and reproduction research being conducted on the pearl oyster, with research targeted at producing viable stocks through breeding programs utilizing controlled reproduction. The commercially utilized method for the production of pearls is nucleus insertion operation, also known as the grafting operation. The success of these controlled reproduction and the nuclei insertion operation is highly dependent on the state of the gonads and mainly gametogenesis. Generally, the sex of an organism is determined by two factors; either genetic or environmental. sox 9, foxl 2, Gata-type zinc finger protein I (zglp1), Protein ovo (ovo) and the dmrt genes are involved in genetic sex determination of pearl oysters. Factors such as hormone administration, temperature, pollution, and culture conditions affect sex determination, and sometimes cause sex reversal of pearl oysters. In pearl oysters, gender has been reported to affect nacre formation and pearl quality. Pearls from males have uniform thickness and smoothness whiles those from females have several scratches. Nacre formation has also been reported to be associated with ovarian development. Sex determination in pearl oyster is therefore an essential mechanism to understand.
Transcriptome analysis of gonads and brain of giant freshwater prawn (Macrobrachium rosenbergii): screening and validation of genes related to germ cell development
2022, Frontiers in Marine Science
How cultured pearls acquire their colour
2020, Aquaculture Research
Sex-changing patterns of Akoya pearl oyster (Pinctada fucata)
2018, Zoological Letters

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Aquaculture

Highlights

Abstract

Introduction

Section snippets

Relationship between sex and pearl yield rate

Cultured pearl quality from male and female Akoya pearl oysters

Characteristics of the pearls cultivated from male and female Akoya pearl oysters

Discussion

Acknowledgments

References (18)

Color and weight of pearls produced by grafting the mantle tissue from a selected population for white shell color of the Japanese pearl oyster Pinctada fucata

Aquaculture

Classification and identification of bacteria by Fourier-transform infrared spectroscopy

J. Gen. Microbiol.

Gene expression patterns in the outer mantle epithelial cells associated with pearl sac formation

Mar. Biotechnol.

Comparison of expression patterns of shell matrix protein genes in the mantle tissues between high- and low-quality pearl-producing recipients of the pearl oyster, Pinctada fucata

Zool. Sci.

Can the quality of pearls from the Japanese pearl oyster (Pinctada fucata) be explained by the gene expression patterns of the major shell matrix proteins in the pearl sac?

Mar. Biotechnol.

Transcriptome and proteome analysis of Pinctada margaritifera calcifying mantle and shell: focus on biomineralization

BMC Genomics

Evaluating and identifying pearls and their nuclei by using optical coherence tomography

Opt. Express

Reproduction-related genes in the pearl oyster genome

Zool. Sci.

Pearl microstructure and expression of shell matrix protein genes MSI31 and MSI60 in the pearl sac epithelium of Pinctada fucata by in situ hybridization

PLoS One

Cited by (6)

The influence of donor and recipient oyster red and blue shell nacre interference color on Pinctada fucata martensii pearl quality

The effects of nacre microstructure on green and pink interference colors in Pinctada fucata martensii pearls

Sex determination in pearl oyster: A mini review

Transcriptome analysis of gonads and brain of giant freshwater prawn (Macrobrachium rosenbergii): screening and validation of genes related to germ cell development

How cultured pearls acquire their colour

Sex-changing patterns of Akoya pearl oyster (Pinctada fucata)