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Title: LOX FOR THE SOCKS: REDUCING WEIGH-BACKS WITH LIQUID OXYGEN

Author
item Torrans, Eugene
item HOGUE, JR., CHARLES - MSU
item PILKINTON, SAM - PILKINTON BROS. FARMS

Submitted to: Catfish Farmers of America Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 12/5/2002
Publication Date: 2/21/2003
Citation: Torrans, E.L., Hogue, Jr., C.D., Pilkinton, S. 2003. LOX FOR THE SOCKS: REDUCING WEIGH-BACKS WITH LIQUID OXYGEN [Abstract]. In: Research and Review; A Compilation of Abstracts of Research on Channel Catfish. Catfish Farmers of America Catfish Culture Research Symposium, February 21, 2003, Sandestin, Forida. p. 54.

Interpretive Summary:

Technical Abstract: Channel catfish are harvested with seines pulled by tractors and hydraulic seine reels. In the final stages of harvest, the fish are concentrated in a sock and often held overnight to allow sub-marketable fish to grade out. Over 50,000 pounds of catfish may be held in a sock at densities over 20-lbs./cu.ft. Sock grading works well most of the year. But when water temperatures are high and D.O. is low (in some cases it may be less than 0.5 mg/L), substantial mortality can occur. Every farmer has a horror story about losing an entire sock of fish to low oxygen. Paddlewheels will increase D.O. slightly, but they also increase water velocity through the sock, greatly adding to fish stress. After a night of chronic stress (assuming the fish survive the night), the fish are further crowded while loading. This additional stress may result in several hundred pounds of weigh-backs, 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. The Sock Saver was designed to hold three 50-gallon LOX dewars that deliver oxygen through eight 200 SCFH flow meters, each supplying an 8-foot self-weighted bioweave diffuser inside the sock through a 100-ft. oxygen hose. The transfer efficiency of these diffusers has been measured at over 15% in water 3.5 ft. deep. From literature values, it was estimated that this system could meet over 80% of the oxygen demand of 50,000 lbs. of catfish. The entire system cost less than $8400. While it was designed to deliver oxygen at full capacity for nearly 11 hours, in practice flows rarely exceeded 1/3 maximum. At a LOX cost of $0.62/gal., it cost less than $3.00/hr. to operate. A harvest crew used this unit on several farms during the 2002 growing season. They felt it made a major difference in their ability to hold fish overnight. Measurements showed it increased dissolved oxygen up to 0.9 mg/L. They also reported the fish had darker color (blanching of the skin is a sign of oxygen stress in channel catfish) and more energy while being loaded after a night(or two or three nights) in a sock. The Sock Saver has proven to be simple to operate, durable and virtually maintenance-free. Since it does not require a power source, it can be set up anywhere. It has a small footprint and does not interfere with other harvest equipment. While we tested this equipment only with food fish, it should be equally valuable with fingerlings.