DISSOLVED OXYGEN
dissolved oxygen: translation
the amount of oxygen freely available in water and necessary for aquatic life and the oxidation of organic materials. For fish, ideal levels are about 7-9 mg/l and most fish cannot survive levels below 3 mg/l. Cold water contains more dissolved oxygen than warm and water too rich in bacteria and other aquatic organisms may use the oxygen up leaving none for fish. At 5°C brook trout use 50-60 mg of oxygen per hour but at 25°C they require 250-360 mg/hour as their metabolic rate increases. A value of 4-5 p.p.m. of dissolved oxygen is the minimum that will support a diverse fish community and values around 9 p.p.m. are preferred. Abbreviated as DO