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

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

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 0.7-1.4 mg/L per hour. Larger fish use less oxygen than smaller fish. In general, increasing temperature increases oxygen consumption.

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

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

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

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

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

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

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

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

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.

Failure to maintain good Dissolved Oxygen Fish Kills

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