This is the first line of defense in the RAS system, which is used to remove solid particles in the water, such as uneaten feed, feces, and so on. Mechanical filtration equipment is usually adopted, such as drum filter, microstrainers, sand filters, etc. Drum filter can filter out larger particulate impurities, with a filtration precision generally around several tens of micrometers, which can effectively prevent these impurities from damaging subsequent equipment and polluting the water quality.

This is a crucial part of the system. It mainly uses microorganisms to decompose harmful substances in the water, such as ammonia nitrogen and nitrite. The biological filter is a common biological filtration device, and its interior is filled with biological filter media, such as ceramic rings, biochemical balls, etc. These filter media provide attachment and growth sites for beneficial microorganisms like nitrifying bacteria. Through their metabolic activities, the microorganisms convert ammonia nitrogen into nitrate, thus reducing the content of harmful substances in the water.

To ensure sufficient oxygen supply for aquatic products, the RAS system is equipped with oxygenation devices. Commonly used ones include microporous aerators and pure oxygen aeration devices. Microporous aerators can evenly disperse air into the water, increasing the dissolved oxygen content in the water; pure oxygen aeration devices can more efficiently raise the dissolved oxygen level in the water, meeting the oxygen demands of aquatic products under high-density aquaculture conditions.

It is used to kill pathogens such as harmful bacteria, viruses, and parasites in the water, ensuring a healthy aquaculture environment. Ultraviolet disinfection devices and ozone generators are commonly used disinfection equipment. The ultraviolet disinfection device achieves the purpose of disinfection by emitting ultraviolet rays to damage the DNA structure of the pathogens; the ozone generator uses the strong oxidizing property of ozone to kill the pathogens, and after disinfection, ozone will decompose into oxygen on its own, leaving no harmful residues in the water.

In urban environments, land resources are scarce and expensive. The advantage of the Recirculating Aquaculture System (RAS) in efficiently using space stands out. It can establish high-density aquaculture facilities in relatively small indoor spaces, such as warehouses, idle factory buildings, or even the basements of buildings.

Examples: Some seafood restaurants in cities, in order to ensure a stable supply of fresh aquatic products like perch and tilapia, will set up small RAS aquaculture systems near the restaurant. This not only reduces the reliance on long-distance transportation of seafood but also guarantees the freshness and quality of the aquatic products.

For high-market-value aquatic products such as grouper, rainbow trout, and prawns, the RAS system can provide precise environmental control, meeting their strict requirements for water quality, temperature, light, and other growth conditions, which helps to improve the quality and yield of the products.

Examples: In some professional aquaculture farms, grouper is cultivated using the RAS system. By precisely controlling the water temperature between 22-28°C and the salinity around 25‰-35‰, while optimizing water quality and light conditions, the growth rate of the grouper is accelerated, the meat becomes more delicious, and due to the stable aquaculture environment, the incidence of diseases in the grouper is reduced, thus increasing the economic benefits of aquaculture.

Seedling breeding requires extremely high environmental stability. The RAS system can precisely control key factors such as water quality and temperature, providing a good growth environment for seedlings and improving the survival rate and health of the seedlings.

Examples: During the breeding of shrimp seedlings, the RAS system can keep the ammonia nitrogen content in the water at an extremely low level while maintaining the water temperature within a suitable range. For example, for the breeding of Litopenaeus vannamei seedlings, the water temperature is controlled between 28-32°C, which is conducive to the growth and development of the shrimp seedlings, ensuring the quality of the shrimp seedlings and providing high-quality seedlings for subsequent large-scale aquaculture.

In the fields of scientific research and teaching, the RAS system provides a controllable experimental and teaching environment. Researchers can easily set different aquaculture conditions to observe the growth and physiological changes of aquatic products under various circumstances. In teaching, students can also intuitively understand the process and principles of aquaculture.

Examples: In aquatic research institutions, researchers use the RAS system to study the impact of fish growth hormones on growth rates. By setting different hormone levels and other environmental conditions, such as temperature and dissolved oxygen, in the system, and accurately recording the growth data of fish, theoretical support is provided for the innovation of aquaculture technologies.