The long-term effects of three levels of dissolved oxygen (100, 60 and 36% of air saturation) on channel catfish, Ictalurus punctatus, were evaluated under two feeding regimes—a constant rate of 3% of biomass daily and ad libitum. At ad libitum rates (6-week duration) average gains of 159, 124, and 65 g per fish were obtained in tanks containing oxygen at 100, 60 and 36% of saturation, respectively. In both experiments food consumption and efficiency were drastically reduced at 36% oxygen saturation. Survival rates were 100% in all groups, thus suggesting that disease and parasite problems were not enhanced by a hypoxic environment. In these studies catfish did not demonstrate a polycythemic response to hypoxic conditions.