DAO 120:125-141 (2016)  -  DOI: https://doi.org/10.3354/dao03017

Ichthyophonus parasite phylogeny based on ITS rDNA structure prediction and alignment identifies six clades, with a single dominant marine type

Jacob L. Gregg1,2,*, Rachel L. Powers3, Maureen K. Purcell3, Carolyn S. Friedman2, Paul K. Hershberger1

1Marrowstone Marine Field Station, US Geological Survey, 616 Marrowstone Point Road, Nordland, Washington 98358, USA
2School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, Washington 98195, USA
3Western Fisheries Research Center, US Geological Survey, 6505 N.E. 65th Street, Seattle, Washington 98115, USA
*Corresponding author:

ABSTRACT: Despite their widespread, global impact in both wild and cultured fishes, little is known of the diversity, transmission patterns, and phylogeography of parasites generally identified as Ichthyophonus. This study constructed a phylogeny based on the structural alignment of internal transcribed spacer (ITS) rDNA sequences to compare Ichthyophonus isolates from fish hosts in the Atlantic and Pacific oceans, and several rivers and aquaculture sites in North America, Europe, and Japan. Structure of the Ichthyophonus ITS1–5.8S–ITS2 transcript exhibited several homologies with other eukaryotes, and 6 distinct clades were identified within Ichthyophonus. A single clade contained a majority (71 of 98) of parasite isolations. This ubiquitous Ichthyophonus type occurred in 13 marine and anadromous hosts and was associated with epizootics in Atlantic herring, Chinook salmon, and American shad. A second clade contained all isolates from aquaculture, despite great geographic separation of the freshwater hosts. Each of the 4 remaining clades contained isolates from single host species. This study is the first to evaluate the genetic relationships among Ichthyophonus species across a significant portion of their host and geographic range. Additionally, parasite infection prevalence is reported in 16 fish species.


KEY WORDS: Ichthyophonus · Parasite phylogenetics · Internal transcribed spacer · RNA secondary structure prediction · rDNA · Herring · Salmon · Halibut · Shad · Rainbow trout


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Cite this article as: Gregg JL, Powers RL, Purcell MK, Friedman CS, Hershberger PK (2016) Ichthyophonus parasite phylogeny based on ITS rDNA structure prediction and alignment identifies six clades, with a single dominant marine type. Dis Aquat Org 120:125-141. https://doi.org/10.3354/dao03017

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