Courtney A. Grady Rachel L. Thompson Maureen K. Purcell Carolyn S. Friedman Paul K. Hershberger Jacob L. Gregg 2014 A combination of field surveys, molecular typing, and laboratory experiments were used to improve our understanding of the distribution and transmission mechanisms of fish parasites in the genus <i>Ichthyophonus</i>. <i>Ichthyophonus</i> spp. infections were detected from the Bering Sea to the coast of Oregon in 10 of 13 host species surveyed. Sequences of rDNA extracted from these isolates indicate that a ubiquitous <i>Ichthyophonus</i> type occurs in the NE Pacific Ocean and Bering Sea and accounts for nearly all the infections encountered. Among NE Pacific isolates, only parasites from yellowtail rockfish and Puget Sound rockfish varied at the DNA locus examined. These data suggest that a single source population of these parasites is available to fishes in diverse niches across a wide geographic range. A direct life cycle within a common forage species could account for the relatively low parasite diversity we encountered. In the laboratory we tested the hypothesis that waterborne transmission occurs among Pacific herring, a common NE Pacific forage species. No horizontal transmission occurred during a four-month cohabitation experiment involving infected herring and conspecific sentinels. The complete life cycle of <i>Ichthyophonus</i> spp. is not known, but these results suggest that system-wide processes maintain a relatively homogenous parasite population. application/pdf en North Pacific Research Board Distribution and transmission of the highly pathogenic parasite <i>Ichthyophonus</i> in marine fishes of Alaska reports