Coastal Aquaculture and Mariculture (2+1)

Unit 4 - Water and soil quality management

4.1.2.a. Dissolved oxygen

• Dissolved oxygen along with temperature controls the metabolism of fish and invertebrates. Together, these two environmental variables control fish production.
• Although atmosphere contains 21% oxygen gas, it is only slightly soluble in water. Thus, water contains only small amounts of oxygen available for fish respiration.
• The main source of oxygen to water is dissolution from the atmosphere. Phytoplankton and macrophytes also add oxygen to water through photosynthesis. Increasing temperature and salinity reduce the saturation point of DO in water.
• Fish oxygen consumption rates vary with water temperature, DO concentration, fish size, level of activity, time after feeding and other factors.
• Metabolic rates vary by species and are limited by low DO conditions.
• Fish can acclimate to low DO conditions, but these adjustments are slow, taking anywhere from a few hours to several weeks.
• Small fish consume more oxygen per unit weight than larger fish of the same species.
• Oxygen consumption increases when fish are forced to exercise, and metabolic energy demands can cause oxygen consumption to double from one to six hours after feeding.
• In general, warm water species tolerate lower DO concentration than cold water fish.
• Warm water fish die after short term exposure to less than 0.3 mg/L DO. To support life for several hours, a minimum of 1.0 mg/L is required, and 1.5 mg/L is required to support fish for several days. However, for obtaining good production DO levels should be above 5.0 mg/L.