The effects of air versus oxygen addition in a serial water use rearing system were assessed in terms of water quality and fish growth, hematology, and kidney condition. Replicate series of five rearing units, stocked with lake trout Salvelinus namaycush at sites in Wisconsin and Pennsylvania, were provided with either aeration or oxygenation chambers, and the water and fish were monitored for 2 months. As expected, ammonia concentration and water conductivity increased, while mean dissolved oxygen (DO) concentration, total gas pressure, and fish growth were reduced as water was used serially. There were differences in total gas pressure between the aerated and oxygenated water, because the nitrogen-stripping effect of oxygenation resulted in much lower total gas pressure by the end of the series compared with water in similar aerated units. Thus the use of oxygen can be far more effective than use of air for control of dissolved nitrogen and total gas pressure. The authors conclude that the use of oxygen rather than air for control of dissolved oxygen did not cause physiological problems, but neither did it enhance health or increase production.