The powered paddle wheels provide emergency pond aeration

Aerators needed

Problems with low dissolved oxygen concentration become more frequent as stocking density and feeding rates increase. Thus, in intensive aquaculture ponds, small, dedicated mechanical aerators powered by electric motors or internal combustion engines are often installed at the beginning of each crop and operated daily to supplement natural sources of dissolved oxygen. In semi-intensive aquaculture, it is not economical to install dedicated aerators in each pond, but some problems with low dissolved oxygen concentrations can occur during most crops. 

Even with dedicated aeration, low dissolved oxygen concentrations can develop. Episodes of low dissolved oxygen have a rapid onset and often occur unexpectedly. Immediate response to quickly increase dissolved oxygen availability can avoid serious losses from stress and mortality.

Varied solutions

In the early years of channel catfish farming in the southeastern United States, producers quickly learned that sudden dissolved oxygen depletion could kill most of the fish in a pond. They tried techniques such as flushing ponds with well water, driving a boat with an outboard motor back and forth over pond surfaces to provide aeration, pumping oxygenated water from adjacent ponds into ponds with low oxygen, and using portable pumps to shoot the low-oxygen water into the air to effect oxygenation as it fell back on the pond surface. 

All these methods provided a degree of oxygenation and reduced fish mortality. However, none was capable of preventing mortality when dissolved oxygen depletion was severe.

Tractor-powered aerators

In the late 1960s, it was found that the differential and rear axles from a light truck could be used to construct a tractor-powered aerator. This device was attached to a tractor, backed into the pond, and powered by the tractor power take-off (PTO). It splashed a tremendous volume of water into the air to effect aeration and produced a strong water current. 

Oxygen-transfer tests conducted at Auburn University revealed that when the paddlewheel aerator depicted was driven by a 65-hp farm tractor, it transferred about 25 kg oxygen per hour. Larger paddlewheels require a more powerful tractor, but transfer proportionally more oxygen to the water.

Portable and efficient

Because of its great capacity to transfer oxygen to water and generate currents to mix the oxygenated water throughout ponds, a single paddlewheel aerator can prevent fish and shrimp mortality during episodes of extremely low dissolved oxygen concentration in ponds up to 8 ha in area. 

These devices are especially useful because they can be easily and quickly moved from one pond to another as needed. Usually, improvements in dissolved oxygen concentration can be seen within 30 minutes to two hours.