What to Do About Oxygen Depletion in Fish Ponds? Treatment Methods for When Temperatures Are Too High or Too Low

Fish farming is also a matter of knowledge, and the survival of fish is inseparable from oxygen. Generally speaking, the dissolved oxygen in aquaculture water should be maintained at 5-8 mg/L, and at least kept at 3 mg/L. So in summer, when the temperature is too high, or in winter and spring, when the temperature is too low, what should be done about oxygen depletion in fish ponds?

1. Handle it this way when the temperature is too high

1. Regularly add fresh water

Regularly injecting fresh water into fish farming ponds is one of the most commonly used and most economical and practical methods for regulating water quality. Generally, add fresh water once every 7-10 days, adding 15-20 cm of fresh water each time. When the pond water deteriorates rather seriously, water replacement measures should be adopted to maintain good water quality conditions. For ponds mainly farming grass goldfish and red carp, the water color is lighter green than that for silver carp, and new water should be added once every 7-10 days, with the water level raised by 20-25 cm each time. During high temperatures in summer, the pond should be kept at the highest water level as much as possible.

2. Use aerators to increase oxygen

Every pond should be equipped with a dedicated aerator, among which the paddlewheel type is best. Running the aerator to increase oxygen can make the water body convect, increase dissolved oxygen in the water and release toxic gases. Note that it should be turned on at noon on sunny days, in the early morning on cloudy days, and in the middle of the night during continuous rainy weather, with each run lasting 1-4 hours. In addition, when there are signs of fish surfacing for air, the aerator should be turned on in advance to increase oxygen.

3. Regularly stir the bottom mud

Stirring the bottom mud can promote the continuous decomposition of the substrate and indirectly control changes in water quality. Generally, stir once every 10-15 days, and the area stirred each time should be no less than 1/3 of the water body area. The effect is best when stirring at noon on sunny days, but do not stir during stuffy, hot weather with low air pressure.

4. Use drugs for improvement

Some ponds have a high fish density and no conditions for frequent water changes, so quicklime should be applied regularly to regulate water quality and reduce the toxicity of toxic gases such as hydrogen sulfide. Each time, 15 kg of quicklime can be used per mu of pond, mixed with water and splashed over the whole pond, once every 20 days or so. Photosynthetic bacteria have the advantages of purifying water quality and increasing the dissolved oxygen content of the water body, and can also serve as feed for filter-feeding fish, generally splashed over the whole pond once every 20 days. If there are too many zooplankton in the fish pond, trichlorfon can be used to kill them, with 0.3-0.5 mg of the drug per cubic meter of water. When there is too much blue-green algae, copper sulfate can be used to inhibit it, with 0.7 mg of the drug per cubic meter of water. When fish surface for air, oxygen-increasing agents and related drugs can also be used to increase oxygen.

5. Properly apply additional chemical fertilizer

Properly applying additional chemical fertilizer can keep phytoplankton at an appropriate density and in a vigorous living state so as to provide food for the fish. At the same time, phytoplankton can absorb the nutrient salts in the water body and produce oxygen through photosynthesis, thereby improving water quality. Therefore, fertilization in high-temperature seasons should be mainly chemical fertilizer, with less organic fertilizer. Generally, in ponds with clear, lean water quality, apply 2.5 kg of urea and 5 kg of superphosphate per mu each time, once every 5-7 days. If organic fertilizer is to be applied, it must be fully fermented first and then applied in small amounts multiple times.

6. Stock aquatic animals together

Aquatic animals are the “consumers” in the water body, and proper co-stocking can promote the balance of the water body ecosystem and achieve the effect of regulating water quality. For example, co-stocking red carp and golden crucian carp can make full use of the residual organic matter in the water body, greatly reducing the putrefactive decomposition of organic matter at the bottom of the water body and reducing the probability of pollution; co-stocking grass goldfish can ensure sufficient dissolved oxygen in the water body and purify the aquaculture environment.

7. Transplant aquatic plants

As the primary “productivity” of the water body, aquatic plants can control the growth of algae and other organisms in fish ponds and play a very good water-purifying role. Farmers can, according to the actual conditions of the pond and adapting to local conditions, reasonably introduce and transplant aquatic plants such as Hydrilla verticillata, houttuynia, water hyacinth, and duckweed into the water body to regulate water quality and improve dissolved oxygen levels.

2. Handle it this way when the temperature is too low

1. Aeration equipment

Aeration equipment is essential equipment for facility aquaculture. There are many types, mainly microporous aeration for oxygen increase, paddlewheel aerators, waterwheel aerators, inflatable aerators, jet aerators, spray-type aerators, etc. The main purpose of aeration equipment is to increase the dissolved oxygen content in the water. By stirring the water body and promoting upper and lower circulation of the water body, it achieves the effects of aeration for oxygen increase and improvement of water quality.

2. Drainage and irrigation equipment

In facility aquaculture, drainage and irrigation equipment is mainly water pumps, including centrifugal pumps, submersible pumps, axial-flow pumps, mixed-flow pumps, deep-well pumps, etc. The purpose of water pumps is to transport fluids. In aquaculture, they are mainly used to fill and drain ponds, ensuring the different water level requirements for fish at each growth stage; injecting river water or deep-well water to regulate water temperature; injecting fresh water to increase dissolved oxygen in the water, improve pond water transparency, strengthen pond water photosynthesis, and increase pond primary productivity; pumping out excess and aged water from ponds to regulate water quality, salinity and pH value, giving fish a suitable water body living environment.

3. Feeding equipment

Feeders named by their feeding form include centrifugal feeders, pneumatic feeders and drop feeders; feeders named by their material supply method include vibrating feeders, flap-type feeders, screw-type feeders, etc. Feeders can automatically feed at fixed times, fixed frequencies, fixed amounts, fixed points and evenly, and have the characteristics of saving labor and time, reducing feed waste, and protecting the water environment.

4. Water quality purification equipment

In facility aquaculture, water quality purification mainly uses biological filter tanks, activated filter tanks and water quality purification machinery, such as biological rotating discs, activated carbon water filtration devices, water cultivators and ozone disinfection and oxygen-increasing machines. Water quality purification equipment can purify and treat harmful substances such as organic matter and ammonia nitrogen in the water.

5. Pond clearing equipment

For ponds that need to be dried in the sun, in order to improve the work efficiency of pond clearing, engineering machinery is mainly selected, such as bulldozers, excavators, transport machines, etc. For dredging in damp ponds with water, dredging machinery is mainly used. Commonly used dredging machinery includes amphibious dredgers, trailing suction dredgers, high-pressure hydraulic cleaning machines, pond digging units and underwater dredgers, etc. Their main function is to cut, collect, extract and transport the sludge in fish ponds to a specific place.

6. Water quality testing instruments

Water quality testing instruments mainly include dissolved oxygen meters, pH meters, water thermometers, ammonia meters, etc., used to test whether the pond water quality conditions meet fishery water quality standards.

7. Water temperature control equipment

Water temperature control equipment includes boiler systems, electric heaters, solar heaters, heat pumps, heat exchangers, automatic water temperature control systems, etc. Its main function is to regulate the water temperature of fish ponds and promote rapid growth of fish at the optimal water temperature.