TRANSPORTING FISH 



often prove fatal to many of the flsh. As 

 a n)eans of reducing this loss, a 24-hour 

 "hardening" process is employed. The 

 fish to be transported are collected and 

 placed in a tank where the water tem- 

 perature can gradually be reduced until 

 it is between 50° and 60° F. The fish 

 are left in this bath for about 24 hours 

 for conditioning. At the end of this pe- 

 riod, they are transferred to transport- 

 ing tanks that contain water of the same 

 temperature and are ready for moving. 

 People who use this technique claim that 

 the fish will not only stand the trip bet- 

 ter but will tolerate more handling and 

 crowding than before hardening. 



2. To prevent injury to the fish, the 

 wooden sides of the tank should be 

 smooth. Several types of tanks have 

 proved satisfactory. One popular type 

 is a single-compartment tank, 4 feet 

 square and 3 feet deep, aerated with oxy- 

 gen dispersed through a perforated re- 

 lease tube. This tank will carry 125 

 pounds of minnows for 300 or 400 miles 

 with little or no loss. Another success- 



ful tank is 6 feet long, 3 feet wide, and 

 iy<i, feet deep. This tank is divided into 

 two compartments, each of which will 

 hold 100 pounds of minnows. It has the 

 advantage of permitting the dealer to sort 

 his fish either by species or by size 

 (fig. 24). 



3. Carrying tanks must be well aerated 

 either by injecting oxygen into the water 

 or by pumping the water through pres- 

 sure jets. Under full load, any system 

 used should maintain a minimum of 3 

 p. p. m. of dissolved oxygen for the dura- 

 tion of the trip. 



All carrying tanks used on long hauls 

 should have two aerating devices that 

 can be operated independently of each 

 other, in case one breaks down. An oxy- 

 gen tank can be substituted for one pump 

 in most cases. 



Aeration is sometimes obtained from 

 wind scoops and water pumps driven by 

 the truck motor. Both of these methods 

 depend for their success on the ability of 

 the truck to maintain motion. When the 

 truck breaks down the fish are out of oxy- 



FiGUBE 24. — An inexpensive fish-distribution tank truck. (Photograph courtesy of 

 the Minnesota Department of Conservation.) 



41 



