In the aquaculture industry oxygen levels in water are referred to in (ppm) or percent saturation Nitrogen is usually referred to as percentage of saturation. Fish use a certain amount of oxygen per pound of food for metabolism and need a certain minimum amount of oxygen to maintain life. Fish do not need nitrogen and if the level of nitrogen is above saturation (equilibrium) the nitrogen pressure may become harmful to the fish if high enough, (Popeye disease). Changes in atmosphere, pressure or temperature will cause the dissolved gas content of the water to change. The direction of change will always be toward equilibrium. If the composition of the atmosphere is changed while maintaining 68 degrees F and standard pressure to 40% oxygen and 60%nitrogen, from the air composition of 20% oxygen and 79% nitrogen, the corresponding levels of the two dissolved gases would be 18.2 PPM oxygen and 11.2 PPM nitrogen. If the pressure is changed, for instance, to 1 1/2 atmospheres or 21 psi, from 14.7 psi, (still at 68 F), with gas levels at normal conditions (20% oxygen and 79% nitrogen) the corresponding dissolved gas levels in the water would be 1 112 times that at 1 atmosphere. Dissolved oxygen (DO) would be 13.65 PPM and nitrogen would be 1 1/2 times 14.9 or 22.35 PPM If the water is subjected to atmospheric pressure below one atmosphere-(14.7 psi), as at. Above sea level, the dissolved gas levels within the water will be reduced. Thus dissolved gas levels at Seattle will be higher than at Leadville, Colorado. If the temperature is changed the dissolved gas levels will change. As the temperature increases, the amount of gases at equilibrium in the water will decrease. Saturation in southern California with warmer water will be lower than at Rifle, Colorado. For example, at equilibrium (Saturation) dissolved oxygen level at 68 degrees F is 9.1 PPM At 80 degrees F under the same conditions, the oxygen level is just 8 PPM and the nitrogen level falls to 13.28 PPM This change caused by temperature change is calculated by using a factor known as Bunsen's coefficient. Mr. Bunsen developed tables that can be used L-n calculate the changes in dissolved gases in relation to changes in temperature. The main use of the Bunsen coefficient is to convert mg/L of DO to mm of pressure. See Colt (1984) for complete discussion of this.