Language selection


The effects of prior exposure and body size on the intensity of Kudoa thyrsites infections in Atlantic Salmon



The parasite Kudoa thyrsites is the cause of soft-flesh syndrome in post-harvest Atlantic Salmon farmed in British Columbia. Infected fish exhibit no clinical signs of disease, but the affected muscle rapidly deteriorates after processing. These infections can cause substantial economic hardship to the salmon aquaculture industry with some sites estimating a 10% loss of annual yield, resulting in losses of between $6-10 million. Currently, there are no vaccines or approved strategies for treatment (e.g., chemotherapeutic intervention) for K. thyrsites.

Earlier ACRDP research revealed geographic variation in the prevalence and intensity of K. thyrsites in Atlantic Salmon reared at different seawater production sites. This research discovered that infections typically resolve between six and 12 months following laboratory exposure of fish to the parasite, and therefore, the occurrence of infections in harvested salmon after 18 months or more in seawater suggest multiple or ongoing exposures to the parasite during commercial net pen rearing.

Due to the limited number of commercial sites in British Columbia, it is not feasible to avoid salmon production in sites recognized as a high risk to K. thyrsites. However, it has been observed by producers that the occurrence and economic impact of K. thyrsites is reduced if salmon are initially reared in low risk sites, and then transferred to these higher-risk sites.

This project will further investigate options for managing K. thyrsites infections. Firstly, it will test the efficacy of ultraviolet irradiation of seawater as a method to inactivate K. thrysites in the laboratory and further study the influence of prior exposure to K. thyrsites on parasite development during subsequent exposure. The project will also assess the influence of fish size on the prevalence and severity of the infection.

The knowledge gained through this research project will lead to a greater understanding of disease transmission and wild-farmed interactions. Additionally, this information will allow for better finfish cage siting and decision making and the development of tools to help further manage this disease.

This project supports the optimal fish health management objective of the Aquaculture Collaborative Research and Development Program (ACRDP), pertaining to the 2013-14 national ACRDP priority to manage and control pests and pathogens through the understanding of how pests and pathogens can affect the environment and cultured species, and how to manage their impact.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)


2013 - 2015


Pacific: Vancouver Island West Coast

Principal Investigator(s)

Simon Jones

Collaborative Partner(s)

Marine Harvest Canada

Mainstream Canada

Date modified: