Dissolved oxygen (DO) is the most critical and limiting factor in intensive aquaculture. Oxygen enters water through photosynthesis by aquatic plants, principally phytoplankton, and by diffusion at the air-water interface. Diffusion occurs when waters are below saturation, and the greater the deficit between the oxygen concentration in the water and the saturation concentration, the greater the rate of diffusion. In ponds, diffusion is promoted by wind and wave action and by artificial aeration. Oxygen is lost from water through respiration by fish, plankton and other organisms, and by aerobic decay of organic matter. There are distinct diurnal fluctuations of oxygen, with concentrations lowest just after dawn, increasing during daylight hours. This is because of the photosynthetic production of oxygen, (there is also usually more wind during the day) to a maximum in late afternoon, before decreasing again during the night.
Silver perch can tolerate low levels (2 mg/l) for short periods (a few hours) but exposure to sub lethal levels (<3 mg/l) for extended periods will reduce growth and stress fish.
The Signs Fish Exhibit to Low DO
Effects of Low DO
Causes of Low DO
Low DO – What can I do?