Distribution, prevalence, and pathogenicity of the protozoan Perkinsus qugwadi in Japanese scallops, Patinopecten yessoensis, cultured in British Columbia, Canada

Perkinsus qugwadi was detected in cultured Japanese scallops, Patinopecten yessoensis, held for at least 3 months at 5 of 14 locations along the coast of British Columbia. At four of the locations, infected scallops were observed in over half of the samples examined and the prevalence of infection reached 98%. At one location (Cypress Bay), infected scallops were rarely encountered and when infection was present, the intensity was light. Field studies, laboratory experiments, and commercial grow-out operations indicate that high mortalities among Japanese scallops are associated with P. qugwadi infection. Although some scallops responded to infection with an accumulation of numerous haemocytes in the vicinity of the parasite, other scallops appeared not to respond and were overwhelmed by numerous parasites that multiplied in the connective tissues of all organs. Epizootiology of this pathogen in Japanese scallops suggests that P, qugwadi is enzootic in an unknown host in British Columbia, with the introduced Japanese scallop serving as an aberrant host.