Several myxosporean parasites are of importance in fisheries and aquaculture in British Columbia. The PKX organism and Ceratomyxa shasta Noble, 1950 cause disease and mortality, Kudoa thyrsites (Gilchrist, 1924) and Henneguya salminicola Ward, 1919 are of importance because they infect somatic muscle, cause unsightly cysts and soft flesh, and thus reduce the market value of the fish. Myxobolus arcticus Pugachev et Khokhlov, 1979, an apparently non-pathogenic species, along with H. salminicola, is used as a biological tag in fishery management. Myxobolus arcticus has also been used in our laboratory as a model for the study of myxosporean life cycles. Other myxosporeans that have been found in salmonids in British Columbia include Myxobolus squamalis (Iverson, 1954), Myxobolus insidiosus Wyatt et Pratt, 1963, Myxidium truttae Léger, 1930, Myxidium salvelini Shulman et Konovalov, 1966, Chloromyxum sp., Parvicapsula sp., and Sphaerospora sp.