DISSOLVED OXYGEN Management in Catfish Ponds Using Electric Paddlewheel Aerators: New Approaches with Old Technology.

The electric paddlewheel aerator has been the main aerator used in the U.S. catfish industry for the post forty years. While it has its limitations, it is perhaps the most efficient shallow-water aerator yet to be developed. Its shortcomings result not so much from poor design, as from poor usage.

Until recently, most catfish farmers, and perhaps most aquaculturists, believed that if a fish wasn't demonstrating a visible stress response ("topping" or crowding around the aerator), the dissolved oxygen (DO) was adequate, and farmers managed their aeration accordingly. For decades, the goal on commercial catfish farms was to make it through the night without losing a pond to low DO. Dissolved oxygen concentrations in the morning below 1.0 ppm were common during the summer months. Exhaustive research at the National Warmwater Aquaculture Center in Stoneville, MS has proven that premise to be false and that oxygen management strategy to be not only ineffective but costly.

Research has shown that when the morning DO drops below 3.0 ppm, catfish consume less feed, and if it drops low enough that fish crowd around the aerators, feed intake may be reduced by 50% or more, with a comparable impact on growth and production. The challenge then, is to maintain a minimum DO concentration of 3.0 ppm with an aerator that may add only 1.0 ppm to the water that passes through it. Three strategies have been developed to achieve this goal.

1)      With large (10-20 acre) ponds, paddlewheels should not be placed to circulate water around the entire pond. Rather they should be placed to circulate water within about 20% of the pond. By focusing aeration within a smaller area of the pond, DO concentration within that area is slightly higher than if the entire pond was aerated/circulated, and both feed intake and production increases.

2)      Smaller commercial ponds (3-5 acres) can be intensively aerated (5-10 hp/acre) without regard to aerator placement. With intensive aeration these smaller ponds can be completely mixed and aerated.

3)      Split-ponds maximize paddlewheel efficiency by only aerating a small (20% of the total pond area) fish-holding area at night, and allowing DO in the larger wastewater treatment area to fall to 0.0 ppm at night.

Paddlewheel aerators can be fabricated locally in welding shops, are durable and reliable, and can be maintained and repaired in most catfish farm shops. Using the latter two strategies discussed above, 15,000-20,000 lbs/acre of catfish can be produced using only 0.3-0.7 kW-h/lb of fish produced for aeration.

The predicted obsolesce of the electric paddlewheel aerator may be premature, at least for the U.S. catfish industry.