Recirculating aquaculture systems

Recirculating aquaculture systems (RAS) are indoor, tank-based systems in which fish are grown at high density under strictly controlled environmental conditions.

Tank farms use RAS to:

  • reduce reliance on large quantities of water
  • control the environment and water conditions to maintain the health of cultured fish.

You can use RAS where suitable land or water is limited, or where environmental conditions are not ideal for the species being cultured.

Establishment costs

There is a significant cost to establish and operate a viable recirculating system.

We recommend consulting with an engineer to ensure the design is efficient and fits the needs of the species you plan to culture.

Use the Agbiz industry tools for RAS, pond and tank-based systems to help you assess risks and potential costs.

System requirements

Recirculating systems require a higher level of management than pond and tank systems because of the water quality issues associated with high stocking densities and their complex mechanics.

You will need to spend time closely monitoring RAS, and can expect a more labour intensive approach than other aquaculture production systems.


RAS can be used in land-based marine aquaculture, but is more often used in freshwater aquaculture.

RAS operations can be established closer to markets and other infrastructure because of their compact nature and the ability to control environmental conditions.


The design of your system will depend on the specific requirements of the species you want to culture. Most recirculating systems incorporate a biofilter, which removes toxic products (ammonia and nitrites) by a process called nitrification and temperature control.

As you design a recirculating system, consider:

  • water quality requirements
  • stocking density
  • stock size
  • feed types
  • disease.

Water quality

The water in the system is recirculated through tanks and a series of water treatments to remove waste products. Unless the water is correctly treated, the fish will stress, causing:

  • retarded growth
  • increased predisposition to disease
  • eventual death.


Most RAS farmers use a series of 5–10 tonne production tanks connected to a solids removal device and a biological filter. Production tanks vary in size and shape.

Smooth, round tanks with sloping bottoms are useful as solids can be concentrated and subsequently removed from a centre drain. This design facilitates thorough cleaning and ensures aeration is evenly distributed.


In simple recirculation systems, water may be treated by 2 processes:

  • mechanical filtration (to remove solids such as faecal matter, uneaten feeds, etc)
  • biological filtration to remove dissolved toxic wastes.

Other system components

Depending on your location and the species you are planning on farming, consider including other components such as disinfection devices, foam fractionators (or protein skimmers), dedicated aeration units

Support equipment and facilities

You should also make sure you have access to water quality testing equipment, a purpose-built facility to accommodate bulk feeds and hygiene measures to limit the spread of disease.