HATCHERY REQUIREMENTS 



17 



control generally is considered in recycle systems with supplemental make- 

 up water or with egg incubation systems where small quantities of water 

 are required. A number of heat exchange systems are available commer- 

 cially for heating or chilling water. 



AERATION 



Water from springs and wells may carry noxious gases and be deficient in 

 oxygen; lake and river sources also may have low dissolved oxygen con- 

 tents. Toxic gases can be voided and oxygen regained if the water is 

 mechanically agitated or run over a series of baffles. 



STERILIZATION 



Any water that has contained wild fish should be sterilized before it 

 reaches hatchery stocks. Pathogens may be killed by chemical oxidants or 

 by a combination of sand filtration (Figure 5) and ultraviolet radiation. 



BACKWASH TROUGHS 



BACKWASH 

 OUTFLOW 



FILTER TANK 



COLLECTION MAIN FOR CLEAN WATER 

 DISCHARGE AND BACKWASH INFLOW 



Figure 5. Diagram of a sand filter. The water supply is clarified as it flows 

 down through the sand and gravel bed, and is then collected in the perforated 

 lateral pipes and discharged from the filter. The filter is backwashed to clean it 

 by pumping water up through the gravel and sand; the collected waste material 

 is washed out the backwash outflow. 



