Diseases of cultured Japanese scallops ( Patinopecten yessoensis) in British Columbia, Canada

Preliminary grow-out studies with Patinopecten yessoensis in British Columbia, Canada, revealed the presence of at least three pathogens. At one location, the shell boring polychaete, Polydora websteri, was responsible for 84% mortality. Most surviving scallops were stunted and regrowth of the shell was often abnormal. At another locality, a protozoan of unknown taxonomic affinities (SPX) was observed. Following one year of excellent growth and survival (>90%), about 60% of the surviving scallops died within 3 months (June to August). Creamy-white pustules (up to 5 mm in diameter) were observed in 50% of the scallops. SPX was found in the connective tissues of 84% of the scallops with pustules and in 15% of those without pustules. The third pathogen was also an unidentified protozoan (SPG). However, unlike SPX, SPG was found in 5% to 10% of P. yessoensis from seven localities and infections were always light. In addition to the diseases with recognizable causes, focal lesions of unknown aetiology were associated with scallop mortalities (>65%) in six of seven growout localities during 1989–1990. Visible lesions consisting of pinkish-orange pustules (up to 15 mm in diameter) occurred in up to 30% of P. yessoensis. In addition, 30% to 55% of the scallops had microscopic lesions in the connective tissues of all organs.