On Februray 1998 in one of the trout farm of Kohkiloieh & Boyer Ahmad province was observed the mass mortality of trout fry with 3 centimeters total length. The rate of mortality was 40%. The sampling was done randomly from various traphs of hatchery hall and 200 fish fry sampled. Wet smears provided from skin and gill of 100 pieces of fish showed 100%infection to parasite Ichthyobodo which the contamination in skin was severe and about gills, it was moderate. Treatment procedures recommended of increasing water flow, decreasing fish density, formalin bath with proportion of 1:4000 for one hour with use of aeration in order to supplying dissolved oxygen needed (synchronously). Above recommendations were effective in decreasing of contamination load and mortality rate.
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