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Parasites Affecting Atlantic Aquaculture Development



The project focuses on two parasites affecting aquaculture in Atlantic Canada; Prosorhynchus squamatus, a digenean castrator in blue mussels and Haplosporidium nelsoni, "MSX" in American oysters. The infections pose no human health threat, but have impeded aquaculture development due to concerns about transfers from positive sites to unaffected sites (inter- and intra-provincially) and the potential for spread.

The mussel castrator, Prosorhynchus squamatus, is a parasite that can cause castration of the blue mussel (Mytilus edulis), and, in severe infections, weakening and a diminished shelf-life. Although reported from some fish species in Atlantic Canada, it was not detected in mussels until 1997, when high prevalences and intensities were found in samples from the southeastern shore of Nova Scotia. This triggered restrictions on mussel transfers from castrator positive sites, pending a targeted survey to map the geographic extent of P. squamatus in Maritime mussel populations. To this end, a total of 5248 mussels (wild and cultivated) from Nova Scotia, New Brunswick, Prince Edward Island and Magdelan Island were analysed. The parasite was not observed in mussels sampled in 2001 or 2002. A prevalence of 3% was detected in one sample in fall 2003. A prevalence of 3% was also found in a spring 2004 sample. Results suggest that the parasitic mussel castrator is normally a low level and sporadic infection which does not present a significant threat to Atlantic mussel populations. Results also suggest that restrictions on mussel transfers from P. squamatus positive sites should be re-evaluated with respect to infection transfer and impact risk. Regular monitoring of mussels for general health status should be sufficient to detect any changes in the low P. squamatus infection levels observed in this study.

MSX is a notifiable disease of concern listed by the Office International de Épizooties - OIE based on the devastating effects to oyster stocks this disease has caused along the mid-Atlantic coast of the US. Documenting distribution and monitoring mortalities is essential to ensure the most current information is available to fisheries managers and industry to allow aquaculture activities to continue while protecting uninfected stocks.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)


2001 - 2006


Atlantic: Gulf of Maine, Scotian Shelf

Principal Investigator(s)

Mary Stephenson

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