Using microradiography to assess nacre thickness of mabé pearls: Technique suitability and insights

Factors influencing half‐pearl (mabe) production and quality in the red abalone Haliotis rufescens

“…This problem occurred because mantle tissue at the ventral‐distal position folds and does not always cover the nucleus, leaving it partially or totally exposed (Figure e). In support to these findings, a particular position on the shell (posterior region of the left valve rather than the anterior region) was identified as optimal for maximizing mabe quantity and quality in the winged pearl oysters Pteria sterna (Saucedo et al, ) and P. penguin (Gordon et al, , ), in spite of their anatomical differences with abalone. Given these results, we recommend avoiding the ventral position for implanting H. rufescens .…”

“…Mabe quality was also evaluated for shape, colour, lustre and defects using one of the commercial schemes ruling the pearling industry (Gordon et al, ; Ky, Nakasai, Molinari, & Devaux, ): (a) AAA for gems of regular shape, excellent lustre and almost no defects on their surface, such as wrinkles, cracks, bumps or spots; (b) AA for high‐quality pearls with very good lustre and few defects on their surface; (c) A for good‐quality pearls as for shape and lustre and nearly 50% defects; (d) B for regular‐quality pearls with average lustre and considerable defects; and (e) C for bad‐quality pearls as for these traits and no commercial value. The Pearl Grading Manual of the Gemological Institute of America (GIA) was used as support for grading mabe quality traits.…”

“…So far, adapting a technology originally developed for sessile bivalves to motile gastropods such as abalone has required research for overcoming anatomical differences. In pearl oysters, for example, the position of implanted nuclei on the shell is perhaps the most important aspect to consider (Gordon et al, ; Gordon, Malimali, Wingfield, Kurtböke, & Southgate, ; Kishore, Southgate, Seeto, & Hunter, ; Ruíz‐Rubio, Acosta‐Salmón, Olivera, Southgate, & Rangel‐Dávalos, ). As a rule, nuclei placed towards the posterior side of the shell result in more symmetrical mabe than nuclei placed on the anterior side.…”

“…In bivalves, there is a falling point for each oyster producing the maximum number of high quality mabe before their average quality decreases. As a rule, larger pearl oyster species ( P. maxima , P. margaritifera , Pteria penguin ) can receive more nuclei than smaller pearl oyster species ( Pteria sterna , P. fucata, Pinctada imbricata ) before average quality decreases (Gordon et al, , ; Kishore et al, ; Ruíz‐Rubio et al, ; Saucedo et al, ). While most of these technical aspects involved in mabe production are relatively well known in pearl oysters, they are unavailable for abalone (Hutchins, ; Wentzell, ) and are required to optimize the technology for producing high‐quality mabe in these species.…”

“…The position of implanted nuclei in relation to the shell edge or adductor muscle is another key factor to consider. Usually, nuclei placed close to the shell edge are covered with periostracum, favouring a high proportion of asymmetrical, low-quality mabe, while nuclei placed close to the muscle, especially in younger oysters, are covered by this organ during growth, resulting in dull mabe (Gordon et al, 2018;Kishore et al, 2013;Ruíz-Rubio et al, 2006;Saucedo, Monteforte, & Blanc, 1998).…”