270 KISH HATCHERY MANAGEMENT 



in the presence of sunlight and high temperatures and thus are less likely 

 to be effective during summer months than during the cooler months of the 

 year. Mixing chemicals may enhance or intensify the toxicity of one of 

 them. Also, certain chemicals are toxic to plants and can cause an oxygen 

 depletion if used in ponds at the wrong time. 



(4) Disease. Although disease may be a self-evident factor, it is disregard- 

 ed widely, much to the regret of many fish culturists. Most of the chemi- 

 cals used to treat fish diseases are expensive and generally are effective 

 only against certain groups of organisms. Use of the wrong chemical or 

 drug usually means that several days to a week may pass before one real- 

 izes the treatment was not effective. During this time, large numbers of fish 

 may be lost unnecessarily. 



When it is apparent that a treatment is necessary, the following rules 

 must be adherred to: 



(a) Pretreatment Rules 



1. Clean holding unit. 



2. Accurately determine the water volume and flow rate. 



3. Choose the correct chemical and double-check concentration figures. 



4. Prevent leaks in the holding unit if a prolonged dip treatment is 

 involved (see below). 



5. Have aeration devices ready for use if needed. 



6. Make sure of the route by which chemical solutions are discharged 

 from the holding unit. 



(B) Treatment Rules 



1. Dilute the chemical with water before applying it. 



2. Make sure the chemical is well-mixed in the units or ponds. 



3. Keep a close watch on units during treatment period. 



4. Observe fish closely and frequently during treatment (aeration of 

 water may be required). 



5. Turn on fresh water immediately if fish become distressed. 



(C) Post Treatment Rules 



1. Recheck fish to determine success of treatment. 



2. Do not stress treated fish for at least 48 hours. 



Various methods of treatment and drug application have been used in 

 the control of fish diseases. There is no one specific method that is better 

 than others; rather, the method of treatment should be based on the specif- 

 ic situation encountered. 



DIP TREATMENT 



During the dip treatments, small numbers of fish are placed in a net and 

 dipped in a strong solution of chemical for a short time, usually 15-45 



