DAO 89:179-183 (2010)  -  DOI: https://doi.org/10.3354/dao02184

NOTE
Sequence analysis of the internal transcribed spacer (ITS) region reveals a novel clade of Ichthyophonus sp. from rainbow trout

C. Rasmussen1, M. K. Purcell1, J. L. Gregg2, S. E. LaPatra3, J. R. Winton1, P. K. Hershberger2,*

1Western Fisheries Research Center, US Geological Survey, 6505 NE 65th Street, Seattle, Washington 98115, USA
2Western Fisheries Research Center, US Geological Survey, Marrowstone Marine Field Station, 616 Marrowstone Point Road, Nordland, Washington 98358, USA
3Research Division, Clear Springs Foods, Inc., PO Box 712, Buhl, Idaho 83316, USA
*Corresponding author. Email:

ABSTRACT: The mesomycetozoean parasite Ichthyophonus hoferi is most commonly associated with marine fish hosts but also occurs in some components of the freshwater rainbow trout Oncorhynchus mykiss aquaculture industry in Idaho, USA. It is not certain how the parasite was introduced into rainbow trout culture, but it might have been associated with the historical practice of feeding raw, ground common carp Cyprinus carpio that were caught by commercial fisherman. Here, we report a major genetic division between west coast freshwater and marine isolates of Ichthyophonus hoferi. Sequence differences were not detected in 2 regions of the highly conserved small subunit (18S) rDNA gene; however, nucleotide variation was seen in internal transcribed spacer loci (ITS1 and ITS2), both within and among the isolates. Intra-isolate variation ranged from 2.4 to 7.6 nucleotides over a region consisting of ~740 bp. Majority consensus sequences from marine/anadromous hosts differed in only 0 to 3 nucleotides (99.6 to 100% nucleotide identity), while those derived from freshwater rainbow trout had no nucleotide substitutions relative to each other. However, the consensus sequences between isolates from freshwater rainbow trout and those from marine/anadromous hosts differed in 13 to 16 nucleotides (97.8 to 98.2% nucleotide identity).


KEY WORDS: Ichthyophonus hoferi · Rainbow trout · Ribosomal gene complex · ITS1 · ITS2


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Cite this article as: Rasmussen C, Purcell MK, Gregg JL, LaPatra SE, Winton JR, Hershberger PK (2010) Sequence analysis of the internal transcribed spacer (ITS) region reveals a novel clade of Ichthyophonus sp. from rainbow trout. Dis Aquat Org 89:179-183. https://doi.org/10.3354/dao02184

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