356 



FISH HATCHERY MANACJKMENT 



Temperature 



Insulation and ice have been used to control the temperature of transport 

 water. Ice sometimes is difficult to find during a delivery trip and can 

 cause damage to fish and tanks if used in large pieces. The main advantage 

 of ice is its simplicity; it involves no mechanical refrigeration equipment 

 that can break down. 



Refrigeration units are being used increasingly to mechanically control 

 water temperature. Such units are expensive and require careful mainte- 

 nance. Large units easily justify the cost of refrigeration but small systems 

 require additional development before they become economical (Figure 

 111). 



Because temperature is such an important factor, it should be continu- 

 ously monitored and controlled. Electric thermometers are readily available 

 and inexpensive, and provide monitoring of temperature from the truck cab. 



Temperature strongly influences oxygen consumption by fish; the lower 

 the temperature, the lower the oxygen consumption. For each 1°F rise in 

 temperature, the fish load should be reduced by about 5.6%; conversely, for 

 each 1°F decrease in temperature, the load can be increased about 5.6%. 

 Thus, if a distribution tank will safely hold 1,000 pounds of 9-inch trout in 

 52°F water, an increase in temperature to 57°F decreases the permissible 

 load by 27.8%i (5° x 5.56%), or to 722 pounds. If the water temperature is 

 decreased from 52°F to 47°F, the load can be increased by 27.8')(i to 1,278 

 pounds. 



Figure 111. Aluminum elliptical tank with refrigeration unit mounted at the 

 front. Aeration is by gas-driven pumps and pure oxygen. Note air scoops (arrow) 

 for CO2 removal on front and rear of tanks. (Ennis National Fish Hatchery, 



FWS.) 



