RAS: not the only answer!

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Because of increasing challenges from lice, plus pressure on available sites for salmon farms, there’s growing interest in closed containment. And while most attention has been paid to RAS, it’s far from being the only answer.

Canadian company Agrimarine has been designing and building floating semi-closed containment systems for many years, firstly in British Columbia, and subsequently in China.

Its project at Lois Lake in BC has been expanded, and is now the largest steelhead salmon producer in Western Canada using a closed containment facility.

Sean Wilton, Head of Business Development for Agrimarine told SalmonBusiness that the farm they set up in China has now been sold, but it’s still going strong. However, the most exciting current developments are taking place much closer to the birthplace of salmon farming.

They have started a project in Norway, for production of post-smolt, and a second tank is going in shortly – near Kristiansand – with a capacity of 300 – 500k fish per tank.

“We also have experience of RAS systems – we built one for our own hatchery, and have been involved in the engineering of others. So we have first-hand knowledge of where the advantages of the floating Agrimarine system lie: primarily in much lower initial capital costs (1/3 to ½), and very significantly lower energy costs, because we use a low-head, high-flow pump,” said Wilton.

He also acknowledges that there are areas where Agrimarine tanks don’t compare so favorably with RAS: they offer less perfect control over all aspects of the growing environment, and are just as affected by bad weather as conventional net pen farms.

There’s the added disadvantage – for now – that the legislatures in salmon-farming countries count tonnage raised in floating closed containment tanks against current licensed biomass. Land-based RAS units don’t face this restriction.

Keeping coastal jobs
However, there is another way that Agrimarine’s system scores highly: it is optimal for use in the same coastal areas currently occupied by net pen farms, and since these tend to be remote and economically-fragile, the farming jobs are critically important to local communities.

“RAS gives complete control of growing environment, and means that fish can be produced to specified sizes throughout the year, but because of the capital costs of the units, they will almost inevitably be built close to markets, or even close to the major processors. So jobs in coastal communities will be lost.”

Beating off-flavors
And the floating tanks offer an even more significant practical advantage: “Because the fish in our system are getting constantly-changed environmental water, they don’t get the build-up of MIB and geosmin – the most common causes of off-flavors in cultivated fish are 2-Methylisoborneol (2-MIB) and geosmin (GSM),” said Wilton.

“In RAS, you need a depuration process to purge the fish, or you get off-flavors because of these. This has been an ongoing challenge for recirculating systems.”

The Agrimarine system also exploits naturally occurring water temperature stratifications through its dual intake system, which allows the operator to manipulate and optimize in-tank water temperatures, meaning the fish feed better year-round, compared to open net pens. In the summer, when surface temperatures can be high enough to damage fish, cooler water may be drawn from depth to mitigate the negative impacts. In the winter, when surface temperatures may be very low, warmer water may be drawn from depth.

Control of lice

  • How well can lice be controlled using Agrimarine tanks?

“We can largely keep them out of the tanks, by techniques such as drawing the intake water from depth, thus avoiding the upper trophic regions in which sea lice thrive.  There is also evidence that moving oxygenated water repels sea lice. The in-tank water is oxygenated and constantly refreshed. This means that lice levels in the tanks are extremely low to zero – other companies developing floating systems have similar findings.”

  • And how about other environmental challenges like algal blooms?

“Similarly, the tank provides an effective barrier against those. And, of course, the risk of predator attack is greatly lowered, as is the risk of escapes.”

The tanks incorporate integrated oxygen supplementation and control systems, as well as a constant and controllable flow of new water, to give the fish an optimized “current” to swim against. Real-time monitoring of life-support systems is also incorporated.

Agrimarine tank

“The constant, gentle movement of water allows the fish to swim as they would in nature, which results in flesh quality similar to wild fish. And the fish feed is carried around the tank until eaten, simulating natural feeding patterns.  This means they feed well – we get excellent feed utilization.”

  • Since your system means the fish are not held in a factory setting, does this mean that the animal welfare lobby supports you?

“Although the fish in our system are in a more natural environment, we get no support from the animal-welfare lobby, because of stocking densities. These are typically around 65k/m3 in our system. Although densities are likely to be much higher in RAS, to try to justify high running costs, the animal welfare lobby tends to focus on SD to the exclusion of all else, and want an arbitrary density figure,” said Wilton.

“But fish school naturally in the wild. In the Agrimarine tanks, we create an artificial current to keep the fish healthy, and you see them schooling happily against the current. So it sounds like high density, but we find the fish have very good health status. We have never had to use antibiotics.”

Ideal for post-smolts
At present, Agrimarine are in discussion with several of the salmon majors in terms of doing post-smolt work. The target is to grow the fish to around 1k, before putting them into marine net pens.

“Because the fish have been protected when young, they seem to fare better, and have good resistance, when they go to sea,” said Wilton. “So there’s a lot of interest in our tanks for post-smolt.”

“You could sum up the advantages of Agrimarine thus,” he concluded. “You get most of the benefits of closed containment without the extreme costs of RAS, and you can keep the jobs where they are most needed.”