HATCHERY REQUIREMENTS 7 



Figure 3. Electric powered aerators midway in a series of raceways can provide 

 up to 2 ppm more oxygen for increased fish production. This type aerator is 

 operated by a 1 horsepower motor and sprays approximately 1 cubic foot per 

 second of water. Note the bulk storage bins for fish food in the center back- 

 ground. (Courtesy California Department of Fish and Game.) 



in raceways, lower concentrations can be tolerated for short periods. How- 

 ever, if either raceway or pond fish are subjected to extended oxygen con- 

 centrations below 5 parts per million, growth and survival usually will be 

 reduced (Figure 4). 



The lowest safe level for trout is approximately 5 parts per million. 

 Reduced food consumption by fingerling coho salmon occurs at oxygen 



