1. INTRODUCTON TO WATER QUALITY IN AQUACULTURE Unit 4:
Dissolved oxygen/aeration
Auburn University
Department of Fisheries and Allied Aquacultures

2. Dissolved oxygen
Aquatic animals require oxygen, just as air breathing animals do.
The oxygen contained in water is termed “dissolved oxygen”.

3. 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.

4. 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

5. Electronic Determination of Dissolved Oxygen
Accurate
Multiple measurements are done quickly
Need to calibrate meter
Most DO meters now automatically take temperature readings, although altitude and salinity values need to be input manually.
Electronic dissolved oxygen meter

6. Factors affecting dissolved oxygen concentrations
Air-water gas transfer
Sediment oxygen uptake
Animal and plant respiration
Photosynthesis
Oxygen is used by cultured species in the pond, but the primary use of DO is by bacteria and plankton.
Total oxygen consumption by plankton, muds and fish in heavily fed catfish ponds is typically mg/L per hour.
Larger fish use less oxygen than smaller fish.
In general, increasing temperature increases oxygen consumption.

7. o2 o2 Factors affecting dissolved oxygen concentration
Air-water gas transfer
Factors that influence the transfer of oxygen:
Temperature
Elevation
Salinity
Turbulence
atmosphere o2 o2 o2 o2 o2 o2
Under
saturated
Super
saturated
Saturated
water

8. Factors affecting dissolved oxygen concentration
Sediment oxygen uptake
atmosphere
water O2 O2 O2 O2 O2 O2 O2 O2 O2
Bacterial respiration
sediment

9. Factors affecting dissolved oxygen concentration
Animal and plant respiration
C6H12O6 + 6O2  6CO2 + 6H2O + heat energy

10. Factors affecting dissolved oxygen concentration
Photosynthesis
It has already been stated that phytoplankton form the basis of the food web of the pond system, but the effect they have on the gas content of the water is also very important.
The role of photosynthesis and respiration by phytoplankton has a significant effect on pond dissolved gas levels.
During light periods (i.e. daytime), phytoplankton increase O2 in the pond water, while at night, they reduce O2 and add CO2 to the water.
6CO2 + 6H2O + light energy  C6H12O6 + 6O2

11. Daily fluctuation in surface dissolved
oxygen concentration in a fish pond
6 a.m.
midnight
6 p.m.
noon 15 10 5
Dissolved oxygen, mg/L

12. 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.
Epilimnion
High temperature
High dissolved oxygen
Thermocline
Low dissolved oxygen
Low temperature
Hypolimnion

13. Management of dissolved oxygen in ponds
Control phytoplankton - Chemical
Copper sulfate crystals
Aeration
Adjust feeding rate.
Water exchange.
mg/L = TA/100
Copper liquid

14. Management of dissolved oxygen in ponds
Control phytoplankton - Biological
Silver Carp
Nile tilapia

15. Aeration Management of dissolved oxygen in ponds
Aeration is the artificial addition of oxygen to the aquaculture system.
The method to increase DO in the water are using some sort of mechanical device to agitate the water.

16. Failure to maintain good Dissolved Oxygen
Fish Kills

17. End of Unit