320 FISH HATCHERY MANAGEMENT 



Figure 91. Chilodonella, 475 x magnification. (Cour- 

 tesy G. L. Hoffman, Fish Farming Experimental Sta- 

 tion, Stuttgart, Arkansas.) 



fish, particularly channel catfish. Epistylis on salmonids can be controlled 

 with one treatment of 167 parts per million formalin for 1 hour if the water 

 temperature is 55°F or higher, or with 250 parts per million formalin for 1 

 hour repeated twice, if the water temperature is 45°F or lower. For warm- 

 water fish the following treatments have been used: 



(1) Salt (NaCl) at 0.1-1.5% for 3 hours is the best for controlling Epistylis 

 on channel catfish. This is suitable only for raceway, tank, or trough treat- 

 ments, not for ponds. 



(2) In ponds, use formalin at 15-25 parts per million or potassium per- 

 manganate at 2 parts per million. These treatments usually must be 

 repeated two to three times to achieve an effective control. 



TRICHODINA 



Trichodinids are saucer-shap>ed protozoans with ciUa around the margin of the 

 body as they normally are viewed under the microscop>e. These protozoans live on 

 the skin, fins, and gills of fish and, when abundant, cause severe irritation and 

 continual flashing. Salmon yearlings, if left untreated, develop a tattered appear- 

 ance. Secondary bacterial infections may develop in untreated cases. 



