Recirculating Aquaculture System (RAS)

A Recirculating Aquaculture System (RAS) is a modern, intensive method of fish farming that uses a closed-loop system to maintain and recycle water. In RAS, water is continuously cleaned, filtered, and recirculated back into the fish tanks, significantly reducing the need for large water inputs and minimizing waste discharge.

 

Key Features of RAS include:

 

Water Recirculation: Water is continuously filtered and reused, reducing the overall water consumption compared to traditional aquaculture methods.

 

Advanced Filtration Systems: The water passes through various types of filters and treatments, including mechanical filtration to removes solid waste (faeces, uneaten feed) and biological filtration, using beneficial bacteria to convert harmful ammonia (from fish waste) into less toxic nitrate (nitrification process).

 

 UV Sterilisation and Ozonation: Helps control pathogens and maintain water quality.

 

Carbon Dioxide Removal and Oxygenation: Ensures proper gas exchange and maintains optimal oxygen levels for fish health.

 

Controlled Environment: RAS allows for precise control of water quality parameters (temperature, pH, salinity), creating optimal conditions for fish growth.

 

RAS facilities are highly efficient in their use of water and land, and can keep fish or shrimp safe from many of the pathogens or parasites to which they would be exposed in marine or pond aquaculture. This type of farming also makes it possible to grow species such as salmon in parts of the world where they could not thrive in the natural environment.

 

The downside is that RAS farming comes with a high capital cost and an ongoing cost in terms of energy use, although access to a renewable or other low-cost energy source can mitigate this.

 

Fish in a RAS facility are vulnerable to system failure which, if it occurs, can prove catastrophic.

 

RAS farming is, nonetheless, attracting a great deal of capital investment around the world.