Paddlewheel aerators also utilize air-to-water contact to transfer oxygen from the air in the atmosphere to the water body. They are most often used in the aquaculture (rearing aquatic animals or cultivating aquatic plants for food) field. Constructed of a hub with attached paddles, these aerators are usually powered by a tractor power take-off (PTO), a gas engine, or an electric motor. They tend to be mounted on floats. Electricity forces the paddles to turn, churning the water and allowing oxygen transfer through air-water contact. As each new section of water is churned, it absorbs oxygen from the air and then upon its return to the water, restores it to the water. In this regard paddlewheel aeration works very similarly to floating surface aerators.