Language selection


A Search for the Alternative Host of the Marine Myxozoan Parasite Kudoa thyrsites Among Commercial Salmon Farms and Departure Bay, Nanaimo



Farm raised Atlantic salmon and Coho salmon raised in British Columbia are susceptible to infection by the parasite Kudoa thyrsites. Kudoa thyrsites is a myxosporean parasite that, for part of its lifecycle, lives within myocytes of many marine teleosts. Post-mortem flesh quality of farmed Atlantic and coho salmon has been severely impacted by K. thyrsites infections. K. thyrsites produces a cathepsin protease that digests host muscle tissue post-mortem causing different levels of myoliquefaction depending on severity of infection. K. thyrsites infections have caused a tremendous economic disadvantage to salmon producers in British Columbia, Canada. Annelids and bryozoans serve as intermediate hosts of several myxosporean parasites of freshwater fishes, suggesting that a heteroxenous life cycle is typical within the Myxosporea. Actinospores, the myxosporean stage that is infective to fish have most often been reported from aquatic oligochaetes but have also been identified in polychaetes and sipunculids. To date there is only one account of a complete life cycle of a marine myxozoan where the alternative host was identified as a marine polychaete. Although elucidation of marine myxozoan life cycles has proven more challenging compared to those residing in FW, the literature suggests that annelids will play a significant role as intermediate hosts. Identification of the intermediate host of K. thyrsites and of the putative actinospore stages that are infective to fish will permit more systematic analyses of the factors that regulate infection in farmed fish. Completion of the life cycle will further our understanding of the basic developmental biology and pathogenesis of Kudoa thyrsites. Eventually, understanding the factors that influence the distribution and abundance of the intermediate host may be useful in interpreting and/or predicting variations in the distribution of Kudoa infections among farmed salmon populations in BC.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)


2004 - 2005


Pacific: Vancouver Island West Coast

Principal Investigator(s)

Simon Jones

Date modified: