Abstract Among different gases oxygen plays an important role for survival, not only for aerial but also for aquatic animals. In both water (fresh as well as sea), oxygen found in dissolved form and consumed by several living organisms. At 1 atm. pressure dissolve oxygen found as 7.0 mg/l at 35oC but other factors also influence its quantity in the same, like air movement, chemicals, vegetation, organisms, etc. In fresh water ecosystem of sagar and devikund sagar village pond dissolve oxygen noted as 5.0975-7.1375mg/l in summer and 9.032-9.322 mg/l in winter. In all fresh water all organisms utilize dissolved oxygen for their survival. Oxygen in different fresh water get intake by all organisms to accomplish its different biological activities. By respiration, oxygen get consumed by organs and produce several ATP (energy) at cellular level, while in turn oxygen comes out from living being in the form of carbon dioxide. The produced energy utilized by different organs to perform different function like locomotion, reproduction, growth, excretion. The oxygen amount in different fresh water body of same area may differ due to several factors. The low oxygen level (amount) may become lethal to different living being like fishes etc. The harsh climatic condition of this region (dry and hot) also plays a very important role for determination the chemical composition of fresh water. A less amount of oxygen is available for aquatic animals of village pond of desert area Bikaner, in compare to another region. An inverse relation noted between dissolved oxygen and temperature, as DO in water decreases with the increase of temperature level.
Keywords Dissolved Oxygen, Devikund Sagar, Fresh Water Ecosystem etc.