| Parasite | Ichthyophonus hoferi |
|---|---|
| Taxonomy | Opisthokonta, Ichthyosporea, Ichthyophonida |
| Hosts | Salmonid fishes including rainbow trout (Oncorhynchus mykiss) and chinook salmon (O. tshawytscha), Pacific herring (Clupea pallasii), yellowtail (Seriola quinqeradiata), etc. |
| Infection site | Internal organs, muscle |
| Clinical signs | Diseased fish exhibits darkening in color, abdominal distention, exophthalmus, nodules on the internal organs (Fig. 1). |
| Parasitology | Previously, Ichthyophonus hoferi was classified into Zygomycetes (Fungi), but now it is a protozoan (Adl et al., 2005). Binucleate hyphal bodies grow up into thick walled spherical multinucleate bodies (20-125 ƒÊm in diameter). The multinucleate spherical bodies extend the hyphal bodies and produce spores. Fish become infected by ingesting the multinucleate spherical bodies, which germinate and penetrate in the gastric mucosa (Hatai, 2004). |
| Pathology | Diseased fish shows abdominal distention caused by accumulation of ascitic fluid and enlargement of the kidney. White small nodules are formed in the visceral organs. Granulomatous inflammation is observed in the focus (Hatai, 2004). |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | Check the multinucleate spherical body in a wet-mount preparation. |
| Other information | A disease outbreak of Ichthyophonus hoferi occurred in cultured rainbow trout in Japan because fish fed on raw herring infected with the parasite. In North America, wild chinook salmon are affected by I. necator during a spawning migration (Kokan et al., 2004). |
| References |
Adl, S. M., A. G. B.
Simpson, M. A. Farmer et al. (2005): The new higher level classification of
eukaryotes with emphasis on the taxonomy of protists. J. Eukaryot. Microbiol., 52 399-451. Hatai, K (2004): Fungal diseases. Infectious and parasitic diseases of fish and shellfish. (ed. by Wakabayashi, H. and K. Muroga), Koseisha koseikaku, pp. 263-284. (In Japanese)
|
(Photos by T. Awakura)
Fig. 2. Multinucleate spherical bodies (arrows) in the liver.
Fig. 1. Nodules in the kidney caused by Ichthyophonus.
