What is a recirculating aquaculture system?

Breeding pond

• This is the place where fish or other aquatic life grows. The shape, size and material of the culture tank vary depending on the species and scale of the culture. For example, for small-scale ornamental fish farming, small glass or plastic culture tanks may be used, while large-scale edible fish farming may use larger concrete or fiberglass culture tanks.

• The design of the breeding pond should take into account factors such as water fluidity, fish activity space and ease of management.

Filtration system

• Mechanical filtration

  • It mainly removes solid particles in the water, such as leftover bait, feces, etc. Common mechanical filtration equipment includes filter screens, filter cotton, etc. The filter screen can intercept larger particles, and the filter cotton can further filter smaller particles to prevent them from accumulating in the system and affecting the water quality.

  
  

• Biological filtration

  • This is the core part of the recirculating aquaculture system. Biological filtration converts harmful substances such as ammonia nitrogen and nitrite in water into harmless substances through the action of microorganisms. The biological filter or biological filter material (such as bio-balls, ceramic rings, etc.) provides a place for beneficial microorganisms such as nitrifying bacteria to attach and grow. These microorganisms convert ammonia nitrogen into nitrite first and then into nitrate through nitrification, thereby reducing the content of toxic substances in the water.

  
  

• Chemical Filtration

  • Used to remove specific harmful substances in water or adjust the chemical parameters of water quality. For example, activated carbon filtration can absorb organic pollutants, pigments and odor substances in water; ion exchange resin can adjust the hardness and pH of water.

  
  

Oxygen enrichment equipment

• Supplement oxygen to the aquaculture water to meet the needs of fish growth. Common oxygenation equipment includes oxygen fans, microporous aerators, etc. The oxygen fan transports air to the microporous aerator at the bottom of the aquaculture pond through a pipeline, so that the air is released into the water in the form of tiny bubbles, increasing the solubility and diffusion rate of oxygen in the water.

Disinfection equipment

• Used to kill pathogens in water and prevent the spread of diseases. Ultraviolet disinfection is one of the commonly used disinfection equipment. It destroys the DNA structure of microorganisms through ultraviolet radiation, thereby achieving the purpose of disinfection. Ozone generators can also be used for disinfection. Ozone has strong oxidizing properties and can effectively kill pathogens such as bacteria, viruses and parasites. However, when using ozone, it is necessary to control the dosage to avoid harming fish.

Temperature control equipment

• Adjust the temperature of the aquaculture water to keep it within a range suitable for fish growth. For tropical fish farming, heating equipment, such as heating rods or heat exchangers, may be needed to maintain the water temperature at a higher level; while for cold-water fish farming, refrigeration equipment, such as chillers, may be needed to lower the water temperature during high temperatures in summer.

Water Cycle

• The water in the breeding pond first flows out through the drainage pipe and enters the filtration system. After a series of treatments such as mechanical filtration, biological filtration, and chemical filtration, impurities and harmful substances in the water are removed and the water quality is adjusted. Then, the water that has been oxygenated and disinfected returns to the breeding pond through the water inlet pipe, forming a cycle.

Transformation and removal of substances

• During the biological filtration process, ammonia nitrogen excreted by fish is a substance that is toxic to fish. Microorganisms such as nitrifying bacteria grow and reproduce on biological filter materials, and they use ammonia nitrogen as an energy source for metabolism. Ammonia nitrogen is first converted into nitrite by nitrite-transforming bacteria, and nitrite is then converted into nitrate by nitrifying bacteria. Nitrate is relatively non-toxic and can be absorbed and utilized by plants or partially removed by changing water. At the same time, mechanical filtration removes solid waste from the water, chemical filtration adjusts water quality parameters such as pH and hardness, and disinfection equipment prevents the growth and spread of pathogens.

Save water

• Compared with traditional water aquaculture, the recirculating aquaculture system can greatly reduce water consumption. Since water is recycled in the system, only a small amount of water lost due to evaporation, leakage, etc. needs to be replenished, which is particularly important in areas with water scarcity.

Water quality controllable

• It can precisely adjust the temperature, pH, dissolved oxygen, ammonia nitrogen and other water quality parameters of the aquaculture water to create a stable and suitable growth environment for fish. This precise water quality control helps to improve the growth rate, survival rate and quality of fish.

Reduce environmental pollution

• Since the waste generated during the breeding process is processed within the system, the amount of sewage and waste discharged into the external environment is reduced. This helps protect the surrounding water environment and reduce the impact on the natural water ecosystem.

Increase stocking density

• Under the condition of stable and good water quality, the breeding density can be appropriately increased, which helps to increase the breeding output per unit area or volume and increase the breeding benefits.