Pathogenesis of black shell disease and its effects on survival and growth in the noble scallop Chlamys nobilis

Abstract

The parasitic disease of mollusks has severely affected the aquaculture industries around the world, and the infestation of polydorids in commercially important mollusks is a serious problem in aquaculture. The black shell disease of noble scallop Chlamys nobilis often occurs, however, pathogeneses and effects on this scallop are unknown. In this study, two species, Polydora haswelli and Polydora lingshuiensis, were identified based on both morphological characteristics and nuclear 18S rRNA gene sequences. Slice observation showed that the tissues of black shell diseased scallops are abnormal compared to the healthy scallops, indicating that infestation of Polydora affects scallop tissues' structure. Metabolomic analysis of polydorids showed harmful metabolites (such as Microcystin LW, Cyclolinopeptides, and Neurosporaxanthin) were significantly higher than these beneficial metabolites (such as Lablabsaponin I, Notoginsenoside E, Taxoprexin, and Candicidin), suggesting these metabolites may cause detrimental effects on hosts. Pathway enrichment analysis of DEGs indicated metabolic pathways (such as amino acid and fatty acid metabolic pathways) and immune-related pathways (such as vibrio, pathogenic, and virus infection pathways) were significantly enriched, which may influence the nutritional quality and immunocompetence. More importantly, the black shell disease can cause high mortality and slow growth in the scallop. This study is the first investigation on the pathogenesis of black shell disease and its effects on survival and growth in the scallop, which is useful for controlling the Polydora infestation in scallop aquaculture.