TRANSPORTATION OF LIVE FISHES 353 



use. It is noncorrosive, lightweight, and easy to assemble, modify, and 

 remove. 



Friction reduces water flow through a circulation system if there is an 

 excess of pipe fittings. Further, the diameter of piping should not be re- 

 duced within the system except at the spray devices. 



Generators and electric pumps or aerators sometimes are used, especially 

 on larger trucks or trailers with multiple tanks. This eliminates the need 

 for many small engines with all their fuel and maintenance problems. Heat 

 and noise problems are minimized by placing the generator on the rear of 

 the unit. 



A method of circulating water with 12- volt mechanical aerators uses car- 

 bon rods and micropore tubing for dispensing oxygen (Figure llO). Aera- 

 tors alone may not be sufficient to provide the oxygen needed to transport 

 large loads of fish, but a supplemental oxygenation system can increase the 

 carrying capacity of the transportation tank. Some advantages of aerator 

 systems over gasoline- driven water pump systems are: 



(1) Temperature increases from aerators are less than 1°F per hour, com- 

 pared with 2.5°F with pumps. 



(2) Aerators and the oxygen injection system can operate independently. 

 There are advantages to carrying small sizes of certain species of fish on 

 oxygen alone. Oxygen also can be used as a temporary backup system if 

 aerators fail. 



(3) Usually, aerators have fewer maintenance problems. 



(4) Costs of recirculating equipment and aerators strongly favor aerators. 



(5) Use of aerators eliminates the space required between the tank and 

 truck cab for pumps and plumbing, so the overall truck length can be 

 reduced to assure safer weight distribution. The empty weight of a truck 

 with a 1,250-gallon tank equipped with aerators is 14,000 pounds — 2,000 

 pounds less than a similar unit operating with pumps and refrigeration. 



The most efficient tanks have the highest water circulation rates, but cir- 

 culation rates must be balanced with water capacity. Pumping or aerating 

 systems should be able to circulate at least 40"o of the tank water per 

 minute when 8-9-inch salmonids are hauled, though lesser rates are ap- 

 propriate for smaller fish. 



Aeration 



The purpose of aeration during transport is to provide oxygen and to 

 reduce the concentration of carbon dioxide. The exchange of gases 

 between water and the atmosphere is a recognized and important problem 

 in transporting fish. Transport water must contain adequate oxygen, pH 



