AUBURN, Ala.—Aerators have become standard equipment for catfish producers, providing needed oxygen that is often depleted during nighttime hours. A new device developed by researchers in Auburn University's Alabama Agricultural Experiment Station may reduce the use of aerators, especially the emergency use of these devices.
Called a horizonal axial-flow water circulator, this machine consists of a mounting body, or frame, a 36-inch diameter tube, with a four-blade impeller, which is powered by a three-horsepower motor, mounted inside the tube. When submerged, it pushed water horizontally and has been effective in mixing top and bottom water in small pond tests at Auburn and in larger ponds at Mississippi State University. The machine can pump about 10,000 gallons per minute.
During daylight hours, surface water in ponds often is supersaturated with dissolved oxygen, and water at greater depths may have low dissolved oxygen concentrations. "By mixing pond water, a uniform dissolved oxygen profile can be established," according to Claude Boyd, a professor of fisheries and allied aquaculture at Auburn and one of the developers of the water mixing machine.
Boyd explained that oxygen produced by phytoplankton may be conserved by water mixing because the high degree of dissolved oxygen supersaturation normally found at pond surfaces during daylight is eliminated. Circulation of pond water also seems to stimulate phytoplankton growth, which may also stimulate dissolved oxygen production by photosynthesis, according to the Auburn researcher.
The water mixer developed by Boyd's research team is different from an aerator. While aerators add oxygen to the water, the water mixer simply moves water from one level of the pond to another. This provides a more uniform level of oxygen throughout the pond, creating a better growth environment for fish. This helps keep oxygen levels high in bottom water and prevents toxic compounds from forming in mud on the pond bottom.
In large pond tests at Mississippi State University's Delta Research and Extension Center, Auburn researcher Bob Howerton and MSU scientist Craig Tucker found that the water mixer operating at 90 rpm provided optimum mixing of water in a four acre catfish pond. "We found that the mixer reduced the amount of time we needed to run aerators," noted Howerton. "By reducing the operating time of the aerators, it should reduce wear and tear and extend the lifetime of these machines," he said.
In ponds with low oxygen supplies, fish don't eat well, nor convert feed to weight gain efficiently. These fish are more susceptible to disease, and in severe cases, most often occurring during warm summer nights, large numbers of catfish can die from oxygen depletion.
"This water mixing machine is intended to decrease the amount of time fish farmers use their aerators. It won't replace aeration, but if subsequent tests prove some of our early findings, it could save catfish producers time and money associated with frequent use of aerators," Boyd concluded.