Aquaculture issues: Fluctuations in DO concentration

Dissolved oxygen is one of the factors of prime importance in Aquaculture. Dissolved oxygen concentrations fluctuate constantly if proper methods are not used to control it. Within a matter of hours, or sometimes even minutes, dissolved oxygen levels can change drastically from optimum to lethal. This dynamic nature of dissolved oxygen concentration results from following factors:

- Water has a limited capacity to hold dissolved oxygen as oxygen is not very soluble in water.
- The rate of oxygen intake by fishes and the aquatic flora and fauna can become very high,
- Water absorbs oxygen from the atmosphere very slowly

          In the day time oxygen concentration varies because of the amount of algae in the water, sunshine, and pressure. On hot days, there is large amount of algae presence. The algae are making photosynthesis and dissolved oxygen concentration becomes very high. This is not optimal for fishes.

 At night, algae consume the oxygen to breathe so there can be deficiency in DO concentrations. Even in winter when nights are longer and the days are cloudy the amount of oxygen is poor.
Also, high concentration of CO2 inhibits the ability of fishes to breathe oxygen from the water, which can also lead to death.

          Generally farmers believe that when there is less oxygen the fishes come up to the surface gasping for air. However, this is the last stage of Oxygen deficiency. Farmers need to check dissolved oxygen problems in the water and increase the aeration process when the fishes become unusually lethargic and stop feeding.