There are three main sources of oxygen in the aquatic environment: 1) direct diffusion from the atmosphere; 2) wind and wave action; and
3) photosynthesis. Of these, photosynthesis by aquatic plants and phytoplankton is the most important.
Oxygen, derived from photosynthesis, is produced during the day when sunlight shines on the plants in the water. Oxygen levels drop at night because of respiration by plants and animals, including fish. These predictable changes in DO that occur every 24 hours are called the diurnal oxygen cycle

Aquaculture of Tilapia and Pangasius; A Comparative Assessment

Michael V. McGee, PhD
Caribe Fisheries Inc.
Lajas, PR

Tilapia can survive exposure to as little as 0.6 mg / L D.O. for short periods of time and levels of 2.0 mg/ L are adequate to prevent significant stress. However, chronic exposure to D.O. levels below 3.0 mg/L will compromise feed utilization and growth rates as well as disease resistance. Thus, Tilapia are dependent on dissolved oxygen in water. Under conditions of intensive production Tilapia ponds are aerated to increase or sustain dissolved oxygen levels. Although effective, use of mechanical aeration can significantly increase production costs.