Kudoa Thyrsites – Increasing our Knowledge



By Dr. Diane Morrison, Fish Health Director Marine Harvest Canada

December 7, 2010

Kudoa thyrsites is a common fish parasite found in many species of fish in the Pacific and Atlantic Oceans. It poses no human or fish health risks but instead, affects product quality by causing pitting and softening of the fish muscle tissue.

The effects of infection are not seen until after the fish has been delivered to the customer, therefore, the economic impact of Kudoa thyrsites can be substantial.

Kudoa thyrsites was discovered in British Columbia farmed Atlantic salmon in the early 1990’s yet, to date, little is known of its life cycle and how and when fish become infected.

Diagnostic tests for detecting and quantifying infection level have been poor and tools to mitigate infection effects on flesh quality are based on best practices and gut feelings only and therefore less than reliable.

Marine Harvest Canada and the BC Center for Aquatic Health Sciences (BC CAHS) have embarked upon a 3-year, joint research project to increase our understanding of Kudoa thyrsites. In the first year, we will be monitoring 2 sites of 2010 S0 YC smolts – Thurlow and Raynor Island – to investigate when fish become infected and how the infection develops through the production cycle. Infection will be detected by using the best means possible, the highly sensitive PCR testing method. The same test will also be used to look for the infective stage of the parasite and to develop a non-lethal test that allows for the tracking of individual fish through their production cycle.

Additional tests will also be developed to quantify the prevalence and intensity of infection.

What does it all mean? With increased knowledge of the parasite’s life cycle, infective stage, timing and progression of infection, we can start to make management decisions to limit and hopefully avoid infection. In addition, the increased knowledge base may lead to future vaccine and/or improved husbandry strategies.

Dr. Luis Afonso will lead the project and research team for BC CAHS. On behalf of Marine Harvest Canada, Tiffany MacWilliam will work closely with BC CAHS and production site staff to organize transportation, sampling details and logistics. This multi year joint effort with CAHS is part of Marine Harvest Canada’s commitment to eliminating the impacts caused by Kudoa thyrsites.





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