The physiological and transcriptional differences between golden and brown noble scallops Chlamys nobilis

Mollusks are the second Phylum in the Kingdom Animalia, which provide not only high-quality protein but also serves as a viewing function for humans due to the polymorphism in shell colors. However, the mechanisms of the differences in shell colors, especially on scallops, have rarely been studied. In this study, the shell and mantle of two different shell colors (golden and brown) of the noble scallops Chlamys nobilis were analyzed, including their microstructure, pigment content, and gene expression. The results showed that the golden scallop shell is golden from the outside to the inside, while the prismatic and nacreous layers in the brown scallop are lighter in color than the periostracum. Unlike the golden scallop, there was a layer of melanin vesicles at the edge of the brown scallop mantle. The total carotenoids content (TCC) in the mantle and shell of the golden scallop was significantly higher than that of the brown scallops (P < 0.05), but the melanin content was significantly lower than that of the brown scallop (P < 0.05). Candidate genes such as BCDO1, CYP5A, CYP2J, CYBA, EP300, and GNAO were screened from the differentially expressed genes (DEGs), and their differential expression may explain the differences in melanin and carotenoid content between the golden and brown scallops. These findings will help to understand the color polymorphism of noble scallops and provide a basis for further research on the inheritance of noble scallops.