300 



FISH HATCHERY MANAGEMENT 



Figure 79. Lymphocystic virus disease. Note numerous "lymphocystic tumors" 

 on skin of walleye. (Courtesy Gene Vaughan, National Fish Hatchery, Nashua, 

 New Hampshire.) 



No method of treatment is known. Fish with the disease should be re- 

 moved from the population to control the spread of the infection. 



Bacterial Diseases 



BACTERIAL GILL DISEASE 



Bacterial gill disease is a typical stress- mediated disease, and probably is 

 the most common disease of cultured trout and salmon; it also is an occa- 

 sional disease of warmwater and coolwater fish reared in ponds. Sudden 

 lack of appetite, orientation in rows against the water current, lethargy, 



Figure 80. Furunculosis in brook trout. Note large furuncles on body surface of 

 fish infected with Aeromonas salmonicida. (Courtesy National Fish Health Labora- 

 tory, Leetown, West Virginia.) 



