|Hogue, jr., Charles|
Submitted to: Aquaculture America Conference
Publication Type: Abstract only
Publication Acceptance Date: 10/1/2002
Publication Date: 2/18/2003
Citation: Torrans, E.L., Hogue, Jr., C.D., Pilkinton, S. 2003. Providing Liquid Oxygen to Remote Sites on Commercial Channel Catfish Farms. [Abstract]. In: Book of Abstracts. Aquaculture America, February 18-21, 2003, Louisville, Kentucky. p. 294. Interpretive Summary:
Technical Abstract: Channel catfish (Ictalurus punctatus) are harvested on commercial farms in the U.S. with long seines pulled by tractors and hydraulic seine reels. In the final stages of harvest, the fish are concentrated in net "socks" and are often held overnight to allow sub-marketable fish to grade out. Over 50,000 pounds of food-sized catfish may be held in a 10 x 50-100 ft. sock. To provide oxygen, water is slowly moved through the sock with a tractor-powered or electric paddlewheel. When the dissolved oxygen (D.O.) is high, sock-grading works well. But when the D.O. is low (in some cases it may be less than 0.5 mg/L), substantial mortality can occur. Paddlewheel aerators will increase D.O. slightly, but they also increase water velocity through the sock, greatly adding to the metabolic oxygen demand of the fish. After a night of chronic oxygen stress (assuming the fish survive the night), the fish 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 - "weigh-backs" for which the farmer is not paid and also reduces the flesh quality of the processed fish. The authors believed that liquid oxygen (LOX) could be used to increase D.O. in the sock without increasing water velocity, greatly reducing fish losses. A small trailer was designed to hold three 50-gallon LOX tanks (dewars) which deliver oxygen through eight 20-200 SCFH flow meters, each supplying an 8-foot self-weighted bioweave diffuser through a 100-ft oxygen hose. The entire system, including the custom-built trailer, three dewars, flow regulators, diffusers and assorted fittings cost a total of $8333.16. The system was designed to deliver oxygen at full capacity (8 flow meters x 200 SCFH = 13.9 gallons/hr.) for nearly 11 hours. In practice, flows have not exceeded 1/3 maximum capacity. At a LOX cost of approximately $0.62/gal., this "insurance policy" costs less than $3.00/hr. to operate. LOX is now being used on a commercial farm when catfish are held in a sock overnight, and initial reports are positive. The equipment is durable, simple to operate, requires no power source, and is compatible with existing harvesting/loading equipment and methods. Studies of oxygen transfer efficiencies are underway.