How cultured pearls acquire their colour

Abstract

Round nucleated pearls are produced through a surgical operation, where a round nucleus and a mantle tissue ‘saibo’ from donor oyster are inserted into the gonad of the host oyster. The epithelial cells in the mantle tissue proliferate around the nucleus, and thus, the pearl sac is formed. Pearl sac secrets nacre and forms a pearl. The quality and economic value of pearls are assessed by pearl features such as colour, brightness, lustre and shape. Among all these features, colour has been reported as an important economic indicator and has been widely studied by researchers. Generally, pearl colour is affected by the donor oyster which is determined genetically and biological pigments (melanin and carotenoid). Organic matrices, metal ions and other factors have also been reported to influence the colour of a cultured pearl. Recently, multi‐omics methods have been used to study the colour formation of pearl, and some key genes and signal pathways related to the colour formation of pearls have been identified. Nevertheless, the specific mechanism of pearl formation needs further research. The review combines both fresh and sea water pearls focusing on Hyriopsis cumingii and pearl oysters to provide a general overview and understanding for pearl colour formation.

DNA Methylation Analyses Unveil a Regulatory Landscape in the Formation of Nacre Color in Pearl Oyster Pinctada fucata martensii

“…Many studies have demonstrated that the shell color of mollusks is generally attributable to the presence of biological pigments ( Wang et al, 2020 ). Indeed, yellow color components suspected to be carotenoids have been examined in cultured Akoya gold pearls ( Williams, 2017 ).…”

“…Several studies have been conducted to reveal the mechanisms of shell color formation and have identified multiple factors, involved in environmental factors and genetic factors, which contribute to the variability of mollusk shell color. In general, shell color is associated with the presence of shell pigments, mainly melanin, carotenoids, porphyrins, and bile pigments ( Wang et al, 2020 ). The striking color range of some gem-producing Mollusca, such as pearl oysters, has also attracted attention ( Williams, 2017 ), color in pearl oysters is of importance for pearl production.…”

“…The striking color range of some gem-producing Mollusca, such as pearl oysters, has also attracted attention ( Williams, 2017 ), color in pearl oysters is of importance for pearl production. It has been proposed that nacre color formation is under to complex control of multiple factors, not only through the biological pigments (melanin and carotenoids), organic matrices, and metal ions but also through genetic regulation ( Wang et al, 2020 ). However, the underlying regulatory mechanisms remain unclear.…”

Detection of Color Treatment and Optical Brightening in Chinese Freshwater "Edison" Pearls

“…Many of these Edison pearls exhibit intense bodycolors in the three main hue categories: purple, pink, and orange. These pearl colors are affected predominantly by the donor oyster's nacre color, which has been known to be genetically determined and inherited (McGinty et al, 2010;Karampelas and Lombard, 2013;Ky et al, 2014;Wang et al, 2020). For freshwater pearls, it is also known that polyenic pigments (such as unmethylated and partially methylated polyenes) containing various chain lengths of alternating double and single carbon-carbon bonds are responsible for color appearance (Soldati et al, 2008a;Karampelas et al, 2007Karampelas et al, , 2009Karampelas et al, , 2019a.…”

A global synthesis of ecosystem services provided and disrupted by freshwater bivalve molluscs

“…In North America and Europe, intense ‘pearl fishing’ over the past century has led to a steep decline and even extirpations of unionid populations but is now largely banned (Bauer, 1988; Anthony & Downing, 2001; Strack, 2015). Freshwater pearl culture for ornamental purposes is an important economy especially in China and other parts of Asia (Janakiram, 2003; Fiske & Shepherd, 2007), with considerable ongoing research efforts aimed at optimising the culture of high‐quality pearls and nacre (Wang et al ., 2020). Finally, live FBs are commonly used in the ornamental pet trade (Erdoğan & Erdoğan, 2015; Ng et al ., 2016).…”