Abstract: Systems for automatically controlling a supply of oxygen to a fish pond (122) are disclosed. The systems include a primary aerator (126) under the control of a controller (128), as well as a fish monitor (130) for monitoring the activity of fish in the pond. The controller determines whether the monitored activity of the fish is indicative of oxygen depletion in the volume of water and, in response to the determination, activates the primary aerator. In one embodiment, a sample or reference aerator (175) creates an oxygen-rich sub-volume (172) wherein activity of the fish is monitored.