The pathobiology of ectoparasitic protozoans on hatchery-reared Pacific salmon
1996
Urawa, S. (Hokkaido Salmon Hatchery, Sapporo (Japan))
The present study was conducted to determine the occurrence and geographical distribution of external protozoan parasites on hatchery-reared Pacific salmon (chum, pink, masu and sockeye salmon) in northern Japan, and to clarify their potential impact on fish populations, and host-parasite interactions such as the defense mechanism of host fish. A flagellate Ichthyobodo necator and two ciliates Trichodina truttae and Chilodonella piscicola are widespread in salmon hatcheries. The infection experiments indicate that these three protozoan parasites are epidemic pathogens capable of causing large economic losses both in hatchery and wild conditions during the course of artificial salmon ranching. Especially, I. necator infection has high potential to cause mass mortalities among anadromous salmonids during their initial marine life. The virulence of the ectoparasitic protozoans is affected by the mode of attaching and feeding, parasite intensity, host condition, and environments. The ideal goal should be to control parasite infections in hatcheries on the basis of these biological information
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