DAO 126:99-109 (2017)  -  DOI: https://doi.org/10.3354/dao03162

Epizootiology of the ectoparasitic protozoans Ichthyobodo salmonis and Trichodina truttae on wild chum salmon Oncorhynchus keta 

Shinya Mizuno1,*, Shigehiko Urawa2, Mahito Miyamoto1, Hayato Saneyoshi1, Makoto Hatakeyama1, Nobuhisa Koide1, Hiroshi Ueda

1Salmon and Freshwater Fisheries Research Institute, Hokkaido Research Organization, Eniwa, Hokkaido 061-1433, Japan
2Hokkaido National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Sapporo 062-0922, Japan
3Field Science Center for Northern Biosphere, Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0809, Japan
*Corresponding author:

ABSTRACT: Infestations of the ectoparasitic flagellate Ichthyobodo salmonis and the ciliate Trichodina truttae have caused acute mortalities of hatchery-reared juvenile chum salmon Oncorhynchus keta in Hokkaido, northern Japan. This study examined the epizootiology of I. salmonis and T. truttae on wild chum salmon as a possible infection source of the 2 parasitic protozoans in hatcheries. Infestations by both ectoparasites were detected on freshwater-adapted adult and juvenile chum salmon in all 4 rivers examined. This is the first study of an anadromous Pacific salmonid to report infestation of I. salmonis and T. truttae in adults returning for spawning. Among the marine-inhabiting phase of chum salmon, infestation with I. salmonis, but not T. truttae, was observed on adults and juveniles. The 2 protozoans were experimentally transmitted at the same time from wild to hatchery-reared chum salmon juveniles, and caused a high rate of mortality in the hatchery fish. In freshwater, the proliferation rate of T. truttae was greater than that of I. salmonis. These observations show that the euryhaline ectoparasite I. salmonis can infest chum salmon throughout their life cycle, in both river and ocean habitats, whereas T. truttae is able to infest these salmonids only in freshwater. Furthermore, wild chum salmon were shown to be a potential infestation source for both T. truttae and I. salmonis in hatchery fish.


KEY WORDS: Hatchery fish · Ichthyobodosis · Infestation experiment · Pacific salmon · Trichodinosis


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Cite this article as: Mizuno S, Urawa S, Miyamoto M, Saneyoshi H, Hatakeyama M, Koide N, Ueda H (2017) Epizootiology of the ectoparasitic protozoans Ichthyobodo salmonis and Trichodina truttae on wild chum salmon Oncorhynchus keta . Dis Aquat Org 126:99-109. https://doi.org/10.3354/dao03162

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