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