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Liquid oxygen safeguard in harvesting

A relatively unsophisticated concept developed about four years ago remains an option for catfish farmers in rare instances when fish designated for harvest can die due to unexpected depleted oxygen levels in the water.

Dubbed a Sock Saver, the system relies on funneling liquid oxygen from tanks into ponds as a way to compensate for substantial oxygen loss. The plan was collaboratively developed about four years ago by Les Torrans, research biologist at the USDA ARS Catfish Genetics Research Unit in Stoneville, Miss., and Columbus, Miss., farmer Sam Pilkinton. The design is not patented.

Torrans said the Sock Saver is loosely viewed as an “insurance” apparatus for growers.

“Every catfish farmer is familiar with the risk when fish are held in socks for extended periods of time while awaiting shipping to fish processors, though it’s something they likely don’t want to talk about,” he said. “The sock holds fish until ready for grading, and 98 times out of 100 that typical system works well. But sometimes, the oxygen level in the pond gets too low,” he said.

While farmers tend to count on paddle wheels run off of tractors to raise the oxygen level in ponds when needed, there can be an adverse effect if several thousand pounds of fish are densely squeezed together in a net during that time, Torrans explained.

The result puts fish in a “marathon-like condition,” he said. “It prompts the fish to swim faster, and eventually they run out of energy.

“The only solution in that instance is you don’t harvest. If you are a larger farmer you can work around it by rescheduling it with another pond ready for harvest, and the plant the fish are to be delivered to will work with you. If you are a larger producer you can do that, you can negotiate with the plant.

“But if you’re a smaller farmer, you get bumped and you don’t harvest that pond and it may be next month until you get back to that plant.”

Such a scenario can often result in an expensive loss, he observed, because typically the loss can be upwards of 50,000 pounds of stock.

“Most farmers, at some point, have lost a whole sack of fish. Sooner or later it’s going to happen,” he said.

In 2000, Torrans wrote an article for an industry journal addressing the problem and proposing an idea that liquid oxygen might be a cogent solution.

Subsequently, he and Pilkinton cooperatively designed the Sock Saver, which Charles Hogue Jr., aquaculture specialist with the Mississippi State Extension Service, helped tweak and promote.

Since then, farmers who have invested in the system, which ranges from $2,000 to $3,000, have held mixed opinions about it.

“Pilkington, for example, says it is one of three huge tools in harvesting fish,” Torrans said. “You don’t need it everyday, but in that rare day you need it, it’s a lifesaver.”

The Sock Saver system developed by the researchers has no moving parts, and functions simply by heating liquid oxygen stored in 50-gallon tanks. The rise in temperature converts the liquid material to gas, which is then directed into the sock area of the pond by a hose.

Because liquid gas is relatively inexpensive (about $1 per gallon) and many growers already use it on their transport trucks, the system is a reasonable investment under ordinary circumstances.

But Torrans said growers have remained reluctant to adopt the system.

“Farmers are really cautious about spending pennies, especially the past few years when fish prices have been so low. It’s tough for them to come up with $2,000 out of their own pockets,” he said.

Torrans insists that using liquid oxygen on fish farms is only in the infant stage of development. “It’s effective but not that efficient. Our tests show that only 15 percent of the liquid oxygen is getting into the water. The rest is bubbling up to the surface.

“While that is OK in these instances, and it does the job, ultimately we are going to get a new piece of equipment that runs off a tractor that will increase transfer into the water.

“Someone will develop that so 90 percent of the oxygen will get into the water, it will be way more efficient.”

He said it appears there is still a waiting period before final judgment on the Sock Saver is made. “There are enough people out there using it now that time will tell whether the Sock Saver catches on in popularity,” he said.

Torrans also observed that using the Sock Saver can alleviate the brooding frustration of losing large amounts of fish in what is generally the final stage of catfish farming.

“With so much time and work involved with the production of the fish — you’ve protected them from birds and disease and you’ve got them in the nets — all you have to do is get them to the plant alive and get your check, and then something like this happens. It’s a heartbreaker.

“Who wants to lose $30,000 worth of fish that is just that far from going to the plant?”


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