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Liquid Oxygen Saves Channel Catfish During Harvest

An improved method for supplying farm-raised catfish with sufficient oxygen during a crucial production stage has been co-developed by an Agricultural Research Service scientist.

Farm-raised channel catfish are harvested with long nets pulled by tractor and hydraulic net reels. In harvesting's final stages, fish are concentrated in net "socks" at high densities and often held overnight to allow smaller, submarketable fish to slip out through the sock mesh.

To provide oxygen, water is slowly moved through the sock with tractor-powered or electric paddle wheel aerators. However, this also increases water velocity through the sock, adding to the metabolic oxygen demand of the fish, which are further crowded to facilitate loading on a transport truck. This additional stress often results in several hundred pounds of dead fish arriving at the plant.

Les Torrans, a research fishery biologist with ARS' Catfish Genetics Research Unit in Stoneville, Miss., says a new system called the "Sock Saver" means more live fish could make it to market. He designed and built equipment to use liquid oxygen (LOX) during harvest with Charles D. Hogue, Jr., of the Mississippi State University Extension Service, and Sam Pilkinton of Columbus, Miss., a catfish farmer and live hauler.

Most private live haulers and fingerling producers now use LOX on their transport trucks, and many farmers use it on their farm trucks when moving fish from pond to pond. The Sock Saver, a small trailer holding three 50-gallon LOX tanks, is hauled behind a pickup truck or a small tractor around commercial ponds to wherever fish are being harvested. Hoses are used to inject pure oxygen through diffusers into a slow water current moving through the sock, increasing dissolved oxygen by as much as 0.9 milligrams per liter.

Research also shows that increasing dissolved oxygen results in faster-growing fish. Techniques for using LOX in ponds during the production cycle will be developed soon.

Read more about this research in the August issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.