Effect of Perkinsus qugwadi on various species and strains of scallops

Japanese scallops Patinopecten yessoensis, introduced into British Columbia, Canada, as a species for aquaculture, proved highly susceptible to an enzootic protistan parasite Perkinsus qugwadi (initially called SPX). Sporadic occurrence of the parasite among cultured scallops sometimes resulted in losses exceeding 90%. Native scallops (Chlamys rubida and Chlamys hastata) were resistant to infection and the pathogenic effects of the parasite. Weathervane scallops Patinopecten caurinus (not amenable to culture but closely related to the Japanese scallop) were not available to test for resistance to infection. Laboratory and field studies showed that first-generation progeny of Japanese scallops that survived an epizootic outbreak of P. qugwadi had a significant increase in resistance to infection and resulting mortalities. Hybrid scallops. resulting from a cross between Japanese scallop females (from the same group of scallops that survived an epizootic outbreak of P. qugwadi) and weathervane scallop males, had similar resistance to P. qugwadi. The identification of scallop stocks that are resistant to P. qugwadi has facilitated the development of a scallop culture industry in British Columbia.