The myxosporean parasite Parvicapsula minibicornis is described from adult sockeye and coho salmon during spawning migrations in tributaries of the Columbia River in Canada and the United States. These observations extend the known distribution of this parasite from the Fraser River drainage basin. The parasite was identified in Columbia River salmonids using polymerase chain reaction (PCR) and by in situ hybridization, but unlike in Fraser River salmon, it was not observed in conventional histological preparations of the kidney. Prevalence of the parasite determined by PCR was higher in spawning sockeye from the Fraser River than in those from the Okanagan River. Our ability to explain the relatively low prevalence and absence of clinical P. minibicornis infections in Columbia River salmon is hampered by our poor understanding of the life cycle of this parasite.

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