INTRODUCTON TO WATER QUALITY IN AQUACULTURE
Unit 4: Dissolved oxygen/aeration
Auburn University
Department of Fisheries and Allied Aquacultures
Dissolved oxygen
• Aquatic animals require oxygen, just as air breathing animals do.
• The oxygen contained in water is termed “dissolved oxygen”.
Dissolved Oxygen
Managing the dissolved oxygen content of the water in a culture system is of critical importance both to keep the animals alive and to increase the production capacity of the system.
Chemical Determination of Dissolved Oxygen
• Accurate
• Water samples can be held for a period of time before measurements
• Time consuming with multiple measurements Dissolved Oxygen Kit
• Accurate
• Multiple measurements are done quickly
• Need to calibrate meter
Electronic Determination of Dissolved Oxygen
Electronic dissolved oxygen meter
Factors affecting dissolved oxygen concentrations
• Air-water gas transfer
• Sediment oxygen uptake
• Animal and plant respiration
• Photosynthesis
Factors that influence the transfer of oxygen:TemperatureElevationSalinityTurbulence
Factors affecting dissolved oxygen concentration
Air-water gas transfer
atmosphere
water
Under
saturated SaturatedSuper
saturated
o2
o2
o2
o2
o2
o2
Factors affecting dissolved oxygen concentration
Sediment oxygen uptake
atmosphere
waterO2
O2 O2
O2
O2
O2O2
O2
O2
sediment
Bacterial respiration
Factors affecting dissolved oxygen
concentration
Animal and plant respiration
C6H12O6 + 6O2 6CO2 + 6H2O + heat energy
6CO2 + 6H2O + light energy C6H12O6 + 6O2
Factors affecting dissolved oxygen
concentration
Photosynthesis
Daily fluctuation in surface dissolved
oxygen concentration in a fish pond
6 a.m. 6 a.m.midnight6 p.m.noon
0
15
10
5
Dissolved oxygen, mg/L
Epilimnion
Thermocline
Hypolimnion
High temperature
High dissolved oxygen
Low dissolved oxygen
Low temperature
Stratification and Dissolved Oxygen
• In a pond, distinctive layers of water may form, with different temperature and DO characteristics.
• This phenomenon can have important implications, especially for deeper ponds.
Management of dissolved oxygen in pondsControl phytoplankton - Chemical
Copper sulfate crystals
Copper liquid
Management of dissolved oxygen in pondsControl phytoplankton - Biological
Silver Carp
Nile tilapia
Management of dissolved oxygen in ponds
Aeration
Failure to maintain good Dissolved Oxygen
Fish Kills
End of Unit