modul Ras System

Introduction to Recirculating Aquaculture System


A land-based Recirculating Aquaculture System (RAS), is a low impact aquaculture process that has the potential to meet the world’s growing need for protein with minimal effect on the environment. Over the past 30 years, the development of Recirculating Aquaculture Systems (RAS) has made it possible to culture fish under completely controlled conditions, anywhere in the world.


The basis of the technology is the recirculation of water inside a land-based fish farming system, whereby the same water is recycled in a closed circuit, thus minimizing the amount of new water that needs to be added to the system.


The team at Assentoft Aqua has been involved in this development since the very beginning of the recirculation aquaculture industry, thus learning from both successes and failures from existing plants, including salmon plants.


Following are the many key benefits of a closed (or RAS) fish farming system:
• Optimal use of feed
• The ability to regulate and control the internal habitat to match the cultured species;
• The ability to reduce invasive fish diseases from the surroundings;
• Easy control of temperature, salinity, oxygen and pH to meet the requirement of both the cultured species as well as the Different growth stages, i.e. whether to induce spawning, wean fish larvae or simply grow fish to market or re-stocking sizes;
• Fast growth of fish during the whole year due to a controlled environment.

The Modul RAS System

Modul RAS is ideal for production of fish between 450 grams up to 2 kg, as this is when the growth rate is at its most rapid and when grading under growth is unnecessary. However, small fish can be graded back to the following batch.


With Modul RAS, the biomass is always at a high amount due to flexible compartments. As only a low percentage of the biomass is harvested, the biomass and feeding are relatively constant, which results in an improved production. Modul RAS also minimizes stress for the fish, as they remain in the same tank for a longer period of time.

The Modul RAS has an integrated water treatment that combine the Mechanical filtration through drum-filters situated over the MBBR. 100% of the water flow is treated in the moving bed bio-reactor and a flexible amount of the flow can pass through two parallel fixed bed bioreactors for removal of fine particles and a degassing unit with counter current cascade for (CO² and N² removal). The water moves via gravitation from the grow-out tanks to the AA cleaning module. Internally in the cleaning unit, the water moves via gravitation which saves energy. The integrated unit takes up a minimum of space and is made of stainless steel.

Modul RAS System
• Smallest footprint – 0.2 HA to 1HA
• Production Capacity  – 400 to 1,200 metric ton/ Year
• Energy efficiency – From 1.5KW onwards per 1kg production
• Auto Harvest
• Patented Dead fish collection system
• Daily harvest
• Standing density – Up to 110kg per m3
• Fish Size Range – From 450 gm to 2kg
• Minimal Manpower

The Assentoft’s Advantage
Assentoft Aqua is second to none in the following :
• Having the lowest possible footprint – saves space, pipes, buildings etc
• Having a fast installation time by using steel tanks as our basic component
• Having the best available water treatment within the industry
• Inventing new creative solutions for the industry
• One of the lowest investment per produced ton of fish
• Deep knowledge about Pelagic fish production in land-based RAS-systems

Fish harvesting

In the Modul RAS system, fish harvesting is simple and with a minimum of stress for the fish. We crowd the fish by moving two gates together. The fish can swim out in a 1 m² opening in the wall. When the gates are 1 m from each other, we lift up a loose bottom screen for a complete harvesting of all the fish in the compartment. Assentoft Aqua has a granted patent on our fish harvesting system.

Dead fish collector

In the Modul RAS System, dead fish are collected by the fish suction arrangement at the inner end of the inclined gate. When a fish dies, it will end at the inner corner of the inclined gate, which means that we can collect the dead fish at a very early stage through an airlift pipe. Assentoft Aqua has a granted patent on our dead fish collector since August 2018.

Movable gates

The key in the Modul RAS system is the movable gates. They optimise the space for the fish when they grow, and they always secure a high amount of biomass. The gates are automatically moved 360° in the raceway by a small motor. Assentoft Aqua has a granted patent for inclined gates; gates that are angled more than 90° from the wall.

Feed systems

Assentoft Aqua can produce and deliver integrated control panels for the plant and thereby supply the feed distribution system. We have a close cooperation with Oxyguard and their Pacific module for the management of water quality.

Feeding augers

Assentoft Aqua produces and sells augers for a wide distribution of the feed. The auger pipe is made of stainless steel.

Feed silos

In cooperation with Assentoft Silo, we supply silos for dry products like fish feed and lime for the aquaculture industry. The product range is from 50 m³ up to 2.000 m³ and mostly in galvanized steel sheet.