How to Regulate Dissolved Oxygen in Fish Ponds? A Full Breakdown of Practical Measures
Regularly add fresh water. Under high-density farming conditions, fish ponds contain more leftover bait and waste, and anaerobic fermentation produces harmful substances such as ammonia nitrogen and hydrogen sulfide, deteriorating the water body. This is especially true in high-temperature seasons, when water quality deteriorates faster. Therefore, regularly adding water is one of the most commonly used and most economical and applicable methods for regulating water quality. Generally, add fresh water once every 7~10 days, adding 15~20 cm of depth each time. When the pond water has deteriorated rather seriously, it is advisable to use water replacement measures to maintain good water quality conditions. In ponds mainly culturing silver carp and bighead carp, the water color should remain grass green or tea brown, with transparency at a water depth of 20~30 cm; in ponds mainly culturing grass carp and common carp, the water color should be slightly lighter than that of silver carp and bighead carp ponds, and new water should be added once every 7~10 days, preferably raising the water level by 15~20 cm each time. In summer, fish ponds should maintain the highest possible water level.
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, with the stirred area each time no less than 1/3 of the water body area, and the effect is best when stirring at noon on a sunny day, but do not stir in muggy weather with low air pressure.
Use aerators to increase oxygen. Intensive ponds should be equipped with dedicated aerators, among which the paddle-wheel type is best. Running the aerator can create water convection, increase the dissolved oxygen content in the water and release toxic gases.
Properly apply chemical fertilizers as topdressing. This can keep phytoplankton at an appropriate density and in a vigorous living state for fish to eat, while phytoplankton can absorb nutrient salts from the water body and produce oxygen through photosynthesis, thereby improving water quality. In high-temperature seasons, fish pond fertilization should mainly use chemical fertilizers and apply less organic fertilizer. Generally, in ponds with clear and lean water, 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 and then used in small amounts multiple times.
Use drugs for improvement. In ponds with high fish stocking density where water cannot be changed frequently, quicklime should be applied regularly to regulate water quality and reduce the toxicity of harmful 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, about once every 20 days. 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, 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 ml per cubic meter of water. If there is too much blue-green algae, copper sulfate can be used to inhibit it, with 0.7 ml per cubic meter of water. When fish show floating-head behavior, oxygen-increasing agents and related drugs can also be used to increase oxygen.
Transplant aquatic plants for improvement. As primary producers in 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 fish pond, adapt measures to local conditions, plan scientifically, and reasonably introduce and transplant aquatic plants such as black algae, houttuynia, water hyacinth and duckweed into the water body to regulate water quality and improve dissolved oxygen levels.
Stock aquatic animals in combination for regulation. Aquatic animals are the “consumers” in the water body. Proper combined stocking can promote the balance of the water body ecosystem and achieve the effect of regulating water quality. For example, combined stocking of common carp and crucian carp can make full use of residual organic matter in the water body, greatly reducing the decay and decomposition of organic matter at the bottom of the water body and reducing the probability of pollution; combined stocking of black carp can inhibit the consumption of various nutrients and oxygen in the water body by organisms such as snails; combined stocking of silver carp can make full use of natural food resources such as plankton in the water body and control water fertility; combined stocking of bighead carp can inhibit rotifers in the water body; combined stocking of grass carp, bream and blunt snout bream can ensure sufficient dissolved oxygen in the water body and purify the farming environment; combined stocking of mandarin fish, snakehead, bass and other fish can effectively control the growth and reproduction of wild miscellaneous fish and shrimp in the water body, reducing the competitive pressure of competing for food and oxygen with the main cultured fish.