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Diseases of Aquatic Organisms

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DAO 58:9-16 (2004)  -  doi:10.3354/dao058009

Ichthyobodo necator (Kinetoplastida) — a complex of sibling species

Jan Arvid Todal1, Egil Karlsbakk1,*, Trond E. Isaksen1, Heidrun Plarre1, Shigehiko Urawa2, Anna Mouton3, Erik Hoel4, Christian W. R. Koren5, Are Nylund1

1Department of Fisheries and Marine Biology, University of Bergen, 5020 Bergen, Norway
2 Research Division, National Salmon Resources Center, 2-2 Nakanoshima, Toyohira-ku, Sapporo 062-0922, Japan
3Western Cape Department of Agriculture, Veterinary Diagnostic Laboratory Services, Private Bag X5020, Stellenbosch 7599, Republic of South Africa
4Aqua-Lab AS, Bontelabo 2, 5003 Bergen, Norway
5Fiskehelsetjenesten i Tromsø, Postboks 2047, 9265 Tromsø, Norway
*Corresponding author; Email:

ABSTRACT: Ichthyobodo necator is a parasitic flagellate that attacks fishes, causing disease problems in freshwater worldwide. Findings of similar flagellates in strictly marine fishes have indicated that ichthyobodiosis may be caused by more than 1 flagellate species. We obtained partial small subunit rDNA (ssu rDNA) sequences of 14 Ichthyobodo isolates originating from fishes in Norway, Japan, Singapore, South Africa and Brazil, and identified 8 strains or species, including 2 species infecting cultured salmon in Norway. An Ichthyobodo species isolated from the skin of Atlantic salmon parr in freshwater is suggested to represent I. necator sensu stricto, while another species, showing particular affinity for the gills, infects salmon in both fresh- and seawater. Atlantic cod is infected with a marine Ichthyobodo species unrelated to those infecting salmonids; 2 cyprinids originating from different parts of the world had related Ichthyobodo strains/species, and 2 isolates from unrelated North and South American fishes were also closely related. The phylogenetic relationships of the Ichthyobodo isolates is described, and the implications of the molecular findings on past and future morphological studies of Ichthyobodo spp. are discussed.

KEY WORDS: Ichthyobodo necator · ssu rDNA 18s · Kinetoplastida · Species complex · Parasitic flagellates

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