special edition: aquaculture feed innovation

Skretting has upgraded its integrated feed concept for RAS

By Jane Byrne

- Last updated on GMT

Skretting RAS R&D facility
Skretting RAS R&D facility

Related tags Salmon diseases Norway smolt RAS

Skretting, a pioneer in diets specifically designed for recirculating aquaculture systems (RAS), has upgraded its integrated feed concept for the closed containment farmed fish production method.

Its new offering is said to take into account growth and waste prediction models for RAS production, nutrient recycling, fish and system health monitoring in addition to the feed raw materials and their impact on the RAS systems themselves.

We spoke to Dr Saravanan Subramanian, global product manager freshwater and transfer feed salmonids, and Evy Vikene, business development manager, salmonids, Skretting, to hear about the principles behind RAS production, the factors to consider in designing a RAS diet, and to see where this farmed fish production model is gaining traction.

How a RAS system works 

To simplify, RAS or closed containment farmed fish production, as it can also be termed, reuses water by running it through a filtration system so it can be used again, said Vikene. 

When it comes to RAS, it is all about control, in terms of fish production and biosecurity, said Subramanian.

“That [level of control] is one of its biggest advantages. RAS also provides a lot of flexibility [in terms of] where you want to produce salmon or other fish; you can farm anywhere, regardless of location, another key advantage, and you can produce more, in a smaller space, in a more efficient way.”

What goes in has to come out

The main inputs into a RAS system are fish and feed, said Subramanian.

“When it comes to traditional systems, the water is just free-flowing. In a RAS system, you need to recirculate the water; the same water has to be reused. All the metabolic nutrients not retained by the fish are released into the water, produced as either solid waste – the feces from the fish - or the dissolved nutrients like ammonia [produced through the gills and the urine].

“These wastes need to be removed from the system to ensure good water quality for the fish. You have to remove the solids as soon as possible. They are removed mainly by two methods, mechanical filtration and bio-filtration, typically drum filters to remove solid particles and biological methods like live microbial filters or aquaponics – plants - to remove ammonia and other dissolved nutrients from the water.”

RAS feed design

In that context, he said it is imperative to use optimal diets to decrease waste output and maximize filtration in order to maintain high quality water conditions, thus improving growth, FCR, product availability and increased biomass. 

Skretting has been operating within this RAS feed space for a long time. 

“RAS feeds are not new for us. We have been in the market since 2009. We were the first company to launch a commercial RAS feed for salmon and other species.

“Globally, we are supplying our RAS feeds to close to 140 RAS sites. 


“One third of our freshwater feeds globally today [are for] RAS.”

In terms of the company’s newly revamped concept for RAS – RecircReady, that is based on a wide set of data, both in house and commercial data, generated over a number of years, he said.

“It is a very holistic concept, that not only incorporates feed, but also fish and system health, and [considers] growth models, waste models and nutrient recycling as well. We need to consider all the factors, to predict the impacts on the system, such as how fast the fish grow, what amount of nutrients will be released, and the impact [of those] on filtration. This enables customers to forecast, to plan their production, so they can enhance the potential of their RAS system.”

Essentials in RAS feed formulation 

“When it comes to RAS feeds, there are three aspects. The digestibility of the raw material nutrients is key. We have a robust in-house NIR system to predict the digestibility of the nutrients. You need to have as digestible a feed as possible.

“The next aspect is the physical quality of the feed. You need a highly water-stable pellet and, of course, you do not want dust and you do not want fat leakage, as that could collapse your mechanical filtration.

“The third aspect is the quality of the nutrients and [their impact on] feces form. You want to ensure you have firm, stable feces, so that they can be efficiently removed by the mechanical filters.  We have an in-house, patented solution to make the feces more stable, so they are easy to remove, thereby, reducing the load on the bio-filter and [ensuring] much better water quality - that will reflect also in the health and welfare of the fish.”

It is about creating consistent, stable feed products, with batch-to-batch variation minimized, he stressed.

Interest in closed fish production systems

Attempts to mitigate the biological risks associated with traditional aquaculture is leading to a lot of momentum for closed fish production systems, all over the world, said Vikene.  

© GettyImages

“You can basically split it [the take-up of RAS production] into the traditional salmon farming markets and the new, emerging salmon producing markets.

“In traditional markets like Norway, Chile, UK, Australia and Canada, based on the biological challenges that are limiting salmon growth there, there is an increasing interest and trend towards producing larger smolt on land.

“Instead of producing a smolt up to 150g – 200g and putting that into open sea cages, producers there are trying to increase smolt size, up to as large as possible. The plan is to increase it up to approximately 1kg, and then put it into open, closed, or semi-closed production.  

“If you are able to produce a 1kg fish on land, you, of course, shorten the time that the fish is at sea, so the fish is less exposed to environmental factors like sea lice, like diseases. [Moreover], new technologies are being developed all the time to improve production in seawater; we see submersible cages, for instance, that can be lowered below the sea lice level.”

There are at least 10-15 existing producers in Norway, alone, that have plans to increase the smolt size on land, said Vikene.  

The main markets for the full salmon grow-out on land are Asia and the US, she said.

“The argument for doing that is you save on freight costs, even if the costs of production are higher. If you have stable prices costs, it makes sense to produce a land-based salmon in a huge market like the US, China and Japan.

There are at least 4-5 relatively big players in those markets that are scaling up in this regard, she said.

Atlantic Sapphire US, a subsidiary of Norwegian farmed salmon firm Atlantic Sapphire A/S, is constructing a land-based aquaculture facility in Miami, Florida, while Pure Salmon is planning to build several RAS facilities to be able to harvest 260,000 tons of Atlantic salmon annually. It said it plans to do it all within the next five or six years.

“The latest analysis I have seen is that, within 10 years, the grow-out land based production will be between 5 and 7% of global salmon production. However, there is huge uncertainty within those numbers.”

‘It boils down to using the resources we have in the most sustainable way’

For Vikene it is not black or white, though, when it comes to making environmental based salmon production choices; favoring RAS over open sea cages at sea is not always to way to go, she argues.

“We think there is room for all seafood products. It is an excellent way of producing protein for a growing population, no matter what production method.

“The traditional salmon producing countries have fantastic resources, [in terms of] their coastlines. We should use the natural resources that we have, and I am fully convinced that with the ability of this industry to innovate, we will be able to grow [salmon production] in a sustainable way.

“For me, it doesn’t make sense to do full grow-out in the traditional markets. However, in the new markets, where there is not [an abundance] of natural resources like coastlines for fish production, it makes sense to do it on land. Recirculating systems are a very efficient way of using water to produce food, if you can get the technology to work and you have the water resources.

“It is not one or the other. There is more than enough room for both production methods – RAS or open cage - because the population is exploding.

“It boils down to using the resources we have in the most sustainable way.”

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