hatchery requirements 43 



Table 5. ammonia and oxygen concentrations in identical circular 

 tanks with high- and low-pressure water systems. tank diameters are 6 

 feet, tank volumes are ,'i30 gallons, flows are 10 gallons per minute 

 (gpm), water changes are 1.13 per hour, fish size is 8.5 inches, and oxygen 

 content of inflow water 8.5 parts per million (ppm). water pressures are 

 pounds per square inch (psi). 



food and excrement toward the center for removal through the outlet 

 screen. Velocity should never be great enough to cause fish to drift with 

 the current. Velocities for small fry may be so low ttiat the tank does not 

 self-clean and it will be necessary to brush accumulations of waste to the 

 center screen. 



Oxygen consumption per pound of fish is higher in circular tanks than 

 in troughs and raceways. This difference may be due to the increased ener- 

 gy demand created by the higher water velocity in the circular tank. 



SWEDISH POND 



The Swedish Pond was developed specifically for Atlantic salmon. It is 

 square with rounded corners and its operation is very similar to that of a 

 circular tank. Water is supplied through a pipe at the surface of the water. 

 Waste water leaves the tank through a perforated plate in the center of the 

 unit and the water level is controlled by a standpipe outside the wall of the 

 tank. This design provides a large ratio of surface area to water volume; 

 some fish culturists feel that Atlantic salmon require more surface area as 

 they do not stack over each other like other salmonids. 



RECTANGULAR TANKS AND RACEWAYS 



Originally rectangular raceways were elongated earthen ponds. Such ponds 

 required considerable maintenance because weeds and plants grew along 

 the banks and the pond walls eroded. Irregular widths and depths resulted 

 in poor water flow patterns. 



Rectangular tanks or troughs generally are used for rearing small fry and 

 fingerlings in the hatchery building (Figure 19). These can be made of 

 aluminum, fiber glass, wood, or concrete. Potentially toxic material such as 



