Shell repair and the potential microbial causal in a shell disease of the pearl oyster Pinctada fucata

The pearl oyster Pinctada fucata is famous for producing luxurious pearls. As filter feeders, they are confronted with various infectious microorganisms. Despite a long history of aquaculture, diseases in P. fucata are not well studied, which limits the development of the pearl industry. We report here a shell disease in P. fucata and a study of the shell repair processes. Scanning electron microscopy (SEM) revealed that the nacreous layer gradually recovered from disordered CaCO3 deposition, accompanied by a polymorphic transition from a calcite aragonite mixture to an aragonite-dominant composition, as revealed by X-ray diffraction analysis. SEM also showed that numerous microbes were embedded in the abnormal shell layers. Similar indications were induced by a high concentration of microbes injected into the extrapallial space, suggesting the potential pathogenic effect of uncontrolled microbes. Furthermore, hemocytes were found to participate in pathogens resistance and might promote shell repair. These results further our understanding of pathogen-host interactions in pearl oysters and have implications for biotic control in pearl aquaculture.