Fish Hatchery Management - fisheries & aquaculture

TRANSPORI'ATION OF LIVE FISHES 353use. It is noncorrosive, lightweight, and easy to assemble, modify, andremove.Friction reduces water flow through a circulation system if there is anexcess of pipe fittings. Further, the diameter of piping should not be reducedwithin the system except at the spray devices.Generators and electric pumps or aerators sometimes are used, especiallyon larger trucks or trailers with multiple tanks. This eliminates the needfor many small engines with all their fuel and maintenance problems. Heatand noise problems are minimized by placing the generator on the rear ofthe unit.A method of circulating water with 12-volt mechanical aerators uses carbonrods and micropore tubing for dispensing oxygen (Figu.e 110). Aeratorsalone may not be sufficient to provide the oxygen needed to transportlarge loads of fish, but a supplemental oxygenation system can increase thecarrying capacity of the transportation tank. Some advantages of aeratorsystems over gasoline-driven water pump systems are:(l) Temperature increases from aerators are less than l'F per hour, comparedwith 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 onoxygen alone. Oxygen also can be used as a temporary backup system ifaerators 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 andtruck cab for pumps and plumbing, so the overall truck length can bereduced to assure safer weight distribution. The empty weight of a truckwith a 1,250-gallon tank equipped with aerators is 14,000 pounds-2,000pounds less than a similar unit operating with pumps and refrigeratron.The most efficient tanks have the highest water circulation rates, but circulationrates must be balanced with water capacity. Pumping or aeratingsystems should be able to circulate at least 409i of the tank water perminute when 8-9-inch salmonids are hauled, though lesser rates are appropriatefor smaller fish.AerationThe purpose of aeration during transport is to provide oxygen and toreduce the concentration of carbon dioxide. The exchange of gasesbetween water and the atmosphere is a recognized and important problemin transporting fish. Transport water must contain adequate oxygen, pH