266 



FISH HATCHERY MANAGEMENT 



A 



B 



Figure 78. (A) Frequently, a fish population (l) must interact with a pathogen 

 (2) in an unfavorable environment (3) for an epizootic (1-2-3) to occur. (B) 

 Interaction of more than three factors may be required. In carp hemorrhagic sep- 

 ticemia, a chronic virus infection (l) of the common carp (2), followed by expo- 

 sure to Aeromonas liquefaciens (3) in a stressful environment (4), may be prere- 

 quisites to an epizootic (1-2-3-4). (Source: Snieszko 1973.) 



Whereas some pathogens of fish are highly virulent and cause disease as 

 soon as they invade a fish, most diseases are stress- related. Prevention of 

 these diseases best can be done through good hatchery management. En- 

 vironmental stresses and associated disease problems are minimized by 

 high water quality standards, optimum rearing densities, and adequate nu- 

 trition. 



Management stresses such as handling, stocking, drug treatments, haul- 

 ing, or rapid temperature fluctuations of more than 5°F frequently are asso- 

 ciated with the onset of several physiological diseases. Table 37 gives a par- 

 tial listing of these fish cultural practices, their associated disease problems, 

 and stress mitigation procedures if known. 



Disease Treatment 



A complete rearing season seldom passes during which fish do not require 

 treatment for one disease or another. Every treatment should be considered 

 a serious undertaking, and caution should be taken to avoid disastrous 



