To maintain healthy fish, DO should be near saturation at any temperature and salinity. Oxygen is diffused into water by various means of aeration: agitation, liquid oxygen, air diffusers (using air compressors and blowers), U-tubes, air stones, and air lifts. A decrease in DO represents a sign of stress in fish. The amount of oxygen a fish requires depends on its life stage, species, size, as well as on the temperature of the water (Tomasso 1993; Tucker 1993). A flow rate of 0.7 x 103 sec1 assures saturation. The U.S. Environmental Protection Agency (EPA 1976) has set 5 mg/L as the minimum DO concentration for optimal fish health.