Shell Nacre Colour is Predictable from Shell Morphometric Measurements in Indian Pearl Mussel Lamellidens corrianus (Lea, 1834)

Identification of nacre properties in live mussels could revolutionize pearl culture industry by aiding selective breeding and cutting down on losses. Indian freshwater pearl mussel Lamellidens corrianus was collected from fifteen different water bodies (375 mussels) spread across the Ganga-Brahmaputra-Meghna river basin for the study. We report for the first time the presence of two nacre colour morphotypes (pink and white, occurring in 1:3 ratio) in the species. Pink shells and white shells had hue angle values between 0 degrees/360 degrees & 180 degrees and 180 degrees & 270 degrees respectively. The mantle tissue of the pink nacred mussels also sported a prominent black "lip" at its anterior edge. Deeper shells with elongated and more acute profiles and sharper shoulders are more likely to have white nacre phenotype with 73% accuracy (P<0.05). Lightness had a strong positive correlation to anterior length and moderate positive and negative correlation respectively to shell width and ligament length. Chroma did not show high correlation to any of the LMI, except for a weak negative (P<0.05) correlation to ventral posterior margin length. However, neither of these continuous colour parameters could be reliably predicted from linear shell morphometric measurements. Our results point to the presence of quantifiable shell shape differences between the two morphotypes. Further studies involving high throughput shell shape phenotyping can potentially enhance the reliability of prediction and can pave the way for phenotypic marker development for nacre quality traits in live mussels.