HATCHERY REQUIREMENTS 41 



Figure 16. Crowding screen used in smaller circular tanks. 



Large circular tanks and pools can be modified with a flat center bottom 

 screen and an outside stand pipe to control water depth for ease of opera- 

 tion. An emergency screened overflow is advisable in the event the bottom 

 effluent screen becomes clogged. Horizontal slots in the drain screens allow 

 better cleaning action and are not as easily clogged as round holes. They 

 also provide more open screen area. Cylindrical center screens used in 

 4-6-foot diameter tanks provide better cleaning action if they are not per- 

 forated in the upper portion, so that all effluent leaves the tank through 

 the bottom portion. 



Self-cleaning properties of the pool are dependent on the angle at which 

 inflowing water enters. The angle of inflow must be adjusted according to 

 the volume of water being introduced and the water pressure (Figure 18). 



The carrying capacity (number or weight of fish per volume of con- 

 tainer) of circular tanks and pools is superior to those of troughs, rectangu- 

 lar tanks, and raceways if there is sufficient water pressure for reaeration. 



