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FISH HATCHERY MANAGEMENT 



Figure 90. Ichthyophthirius on a rainbow trout fin, 6x magnification. (Courtesy 

 G. L. Hoffman, Fish Farming Experimental Station, Arkansas.) 



the appearance of the mature parasites on the fish. Young fish exhibit con- 

 siderable flashing off the bottom and often show erratic spurts of activity, 

 jumping out of the water and thrashing about, due to irritation caused by 

 the parasites. Successful treatment of Ich depends upon the elimination of 

 parasite stages that are free in the water and the prevention of re-infection. 

 Tomites and adult parasites leaving the fish are, therefore, the target of 

 therapeutic efforts. 



The best control for Ich, as for any disease, is prevention. Hatchery wa- 

 ter supplies always should be kept free of fish. If possible, any warmwater 

 fish brought onto a hatchery should be quarantined for at least one week at 

 70°F, and coldwater fish for at least 2 weeks at 60°F, to determine if they 

 i are infested with Ich. 



Ich is difficult to treat because the tissue- inhabiting and encysted forms 

 are resistant to treatment; only the free-swiming forms are vulnerable. Suc- 

 cessful treatment usually is long and expensive. There are several pond 

 treatments for either warmwater fish or salmonids that can be used success- 

 fully if started in time. Copper sulfate can be used at whatever concentra- 

 tion is safe in the existing water chemistry. Treatment is repeated on alter- 

 nate days; usually from two to four applications are necessary, depending 

 on water temperature. This is the least expensive treatment and gives good 



