FISH HEALTH MANAGEMENT 283 



lice, and leeches. The application rate is 0.25 part per million active (0.84 

 pound of 80% W.P. per acre- foot). One treatment will suffice for mono- 

 genetic trematodes, leeches, and fish lice. For effective control of anchor 

 parasites, Masoten should be applied four times at 5-7-day intervals. 



Because Masoten breaks down rapidly at high temperatures and high 

 pH, it may give inconsistent results in summer. If it must be used then, ap- 

 plications should be made early in the morning, and at double strength 

 when water temperatures are above 80°F. 



Equipment Decontamination 



The following procedures for the decontamination of hatchery equipment is 

 taken from Trout and Salmon Culture by Leitritz and Lewis (1976). 



Equipment sometimes must be decontaminated. One of the best and 

 cheapest disinfectants is chlorine. A solution of 200 parts per million will 

 be effective in 30—60 minutes; one of 100 parts per million may require 

 several hours for complete sterilization. Chlorine levels are reduced by 

 organic material such as mud, slime, and plant material; therefore, for full 

 effectiveness, it is necessary to thoroughly clean equipment before it is 

 exposed to the solution. A chlorine solution also loses strength when expo- 

 sed to the air, so it may be necessary to add more chlorine or make up fresh 

 solutions during disinfection. 



Chlorine is toxic to all fish. If troughs, tanks, or ponds are disinfected, 

 the chlorine must be neutralized before it is allowed to drain or to enter 

 waters containing fish. 



One gallon of 200 parts per million chlorine solution can be neutralized 

 by 5.6 grams of sodium thiosulfate. Neutralization can be determined with 

 starch-iodide chlorine test paper or with orthotolidine solution. A few 

 drops of orthotolidine are added to a sample of the solution to be tested. If 

 the sample turns a reddish- brown or yellow color, chlorine is still present. 

 Absence of color means that the chlorine has been neutralized. 



Chlorine may be obtained as sodium hypochlorite in either liquid or 

 powdered (HTH) form. The latter is the more stable of the two, but it is 

 more expensive. The amount of chlorine added to water depends on the 

 percentage of available chlorine in the product used. As an example, HTH 

 powder may contain either 15, 50, or 65% available chlorine. Therefore, the 

 following amounts would be needed to make a 200 parts per million solu- 

 tion: 



2 ounces of 15% available chlorine HTH powder to 10.5 gallons of wa- 

 ter; 



1 ounce of 50% available chlorine HTH powder to 18 gallons of water; 



1 ounce of 65% available chlorine HTH powder to 23.25 gallons of 

 water. 



