HATCHERY REQUIREMENTS 45 



galvanized sheet metal should be avoided. Dimensions of raceways vary, 

 but generally a length:width:depth ratio of 30:3:1 is popular. Properly con- 

 structed raceways have approximately identical water conditions from side 

 to side, with a gradual decline in dissolved oxygen from the head end to 

 the lower end. Levels of ammonia and any other metabolic waste products 

 gradually increase towards the lower end of the unit. Although this 

 represents a deterioration of water quality, some hatchery workers feel that 

 a gradient in water quality might be better for the fish because it attracts 

 them to the higher quality water at the inflow end of the raceway. In circu- 

 lar ponds, there is no opportunity for the fish to select higher oxygen and 

 lower ammonia levels. 



FlGlRF. 1!). Rectangular aluminum troughs (background) and concrete tanks. 

 Small swim-up fry generally are started on feed in the troughs and then 

 transferred to the tanks when they are 1-1 j -inch fingerlings. (FWS photo.) 



