Atlantic Salmon Farm: 28% Higher Survival with Nanobubbles

The grow-out challenge

In a recirculating aquaculture system, aquaculture dissolved oxygen is usually the parameter that decides how much fish you can hold and how quickly it grows. Biofilter performance, CO₂ stripping, ammonia and particle load all matter, but they sit downstream of one question: can you get enough oxygen into the water, reliably, at the density you actually want to run?

Oxygen is not free to add. Conventional ras oxygenation puts gas into water as comparatively coarse bubbles, and coarse bubbles are inefficient by nature — they rise, they reach the surface, and a meaningful share of the gas leaves again without ever dissolving. Operators compensate by pushing harder, which costs oxygen and energy and still leaves gradients through the tank.

The consequences of getting this slightly wrong are familiar on any site. Fish held at low or fluctuating oxygen eat less and convert feed worse. Stress accumulates and shows up as reduced disease resistance. Mortality creeps upward in exactly the part of the cycle where standing biomass is highest and the margin for error is thinnest. And because those losses arrive gradually rather than dramatically, they tend to get absorbed into the definition of normal.

The facility

A land-based RAS facility for Atlantic salmon, operated by a Norwegian salmon producer, with the fish followed through the grow-out phase.

As with our pool reference, the client’s name, exact location and the year of installation are covered by a confidentiality agreement. That is a real limitation on what this page can prove, and we would rather state it than pad around it. What is publishable is the system type, the species, the phase of the cycle and the three figures below.

If you need more than that before you can act — and for a capital decision in salmon farm water treatment, you probably should — ask us for a reference conversation. An introduction to somebody running a comparable site is worth more than any page a supplier can write.

The solution

Nanobubble oxygenation was added to the water treatment loop. The underlying mechanism is the same one used in swimming pools, pointed at a different problem: instead of oxidising organic load, the objective here is to get more oxygen into the water and keep it there.

Nanobubbles are gas-filled bubbles under roughly 200 nanometres across. They are small enough that buoyancy barely acts on them, so they do not rise and vent at the surface the way coarse bubbles do. They remain in suspension, and their combined surface area is very large relative to the volume of gas involved, which is what makes the transfer efficient. The physics is set out on oxygen transfer with nanobubbles.

Two practical consequences matter more than the physics. Oxygen that dissolves instead of escaping is oxygen you paid for and kept. And a suspended bubble population distributes more evenly through the water column than a rising plume does, which reduces the gradients that make fish crowd into the better part of a tank.

What it does not do deserves the same emphasis. Nanobubble oxygenation does not replace a biofilter, CO₂ degassing, particle removal or competent husbandry. It addresses one input — oxygen — very well indeed. If your mortality is driven by pathogen pressure, feed management or handling damage, better oxygenation will help at the margin and will not fix the underlying problem. Any supplier who tells you otherwise is selling.

Results

Three figures are published for this installation. They are large, and a large number deserves a sceptical reading rather than an enthusiastic one — so the table below separates what was recorded from what merely follows from it.

What changed	Before	After	How we know
Survival through grow-out	The site’s established baseline mortality	28% higher survival	Published figure for this installation
Growth rate	Baseline growth for the same phase	Not separately measured	We publish no growth figure for this site — better oxygen availability is expected to help, but we did not measure it
Dissolved oxygen	Conventional oxygenation, with the usual transfer losses	40% higher	Published figure for this installation
Oxygen distribution through the tank	Gradients around the injection point	More even, because the bubbles stay in suspension	Mechanism — not separately measured here
Crowding behaviour	Fish favouring the better-oxygenated zones	Less pronounced	Qualitative
Feed conversion (FCR)	The site’s baseline for the cycle	Expected to improve with growth and survival	Not published for this site — see below

The first three rows are the published figures. The remainder describe the direction of change and are not measurements taken at this facility. One further caveat is worth stating plainly: an improvement of 28% in fish survival rate implies that the baseline had real headroom. That is common in RAS and it is not a criticism of the operator — but it does mean this result should be read as what oxygen limitation was costing this particular site, not as a coefficient you can apply to your own.

Impact on FCR and economics

Feed is the largest single cost in salmon production, so the number most producers actually care about is feed conversion ratio. FCR was not published for this facility, and we are not going to reverse-engineer one — doing that honestly requires assumptions about feed regime, temperature and standing biomass that we do not have.

What can be said is how the published figures connect to the economics. The chain is short enough that you can check it against your own site:

• Survival multiplies everything else. Fish lost late in grow-out have already eaten most of the feed they will ever eat. Late mortality is therefore the most expensive kind, and an improvement in survival lands directly on cost per kilo harvested.
• Growth rate shortens the cycle. Faster growth on the same feed means either more harvests per year from the same tank volume, or the same harvest at a lower standing biomass. Both are worth money; which is worth more depends on whether your binding constraint is volume or licence.
• Oxygen efficiency cuts a direct input cost. Oxygen that dissolves rather than venting is oxygen you do not buy twice, and the energy spent pushing it is not wasted either.
• Stress reduction is real but hard to invoice. Better disease resistance and calmer fish show up as fewer bad weeks rather than as a line in the accounts. Count it as upside, not as the business case.

Taken together, the economic case in aquaculture is usually stronger and faster than the equivalent case in a swimming pool, because the value of the output is high and the losses being avoided are large. It is also considerably easier to prove — provided the baseline is captured before anything changes, which is exactly what we would ask to do on your site.

What we are not publishing, and why

There is no quote from the site manager on this page, no photograph of the tanks, and no company logo. We do not have permission for any of them, and we are not going to invent them.

A named, dated statement from the operator would be the strongest evidence this page could carry, and its absence is a genuine weakness. We would rather you noticed that than have us paper over it with a stock photo and an anonymous sentence in quotation marks. Aquaculture is a small industry with a long memory, and a supplier who publishes a client’s production numbers without clearance does not stay in it for long.

The practical alternative is the one we offer everywhere on this site: ask, and we will request an introduction to an operator. You get an unmediated conversation with somebody who has no reason at all to sell you a system. We publish more references as figures and permission come together, and the pool-side equivalent of this write-up is the resort pool case study.

Want the same result?

Probably not the same numbers — and that is the honest starting point. This result reflects what oxygen limitation was costing one specific facility. Yours may have more headroom or considerably less, and the only way to find out is to measure before you change anything.

The offer is simple. We agree the baseline first: dissolved oxygen at your measurement points, mortality by phase, growth against your own feed data, and oxygen and energy consumption. Then we re-measure the same things at the same points afterwards, on your instruments. If the numbers do not move, you have learned that cheaply and early.

The application detail for tanks, transport, well boats and holding is under live fish transport and aquaculture. Our aquaculture sister company NanoMAR works the same waters, and is worth a look if your questions are entirely fish-side rather than pool-side.

One thing we will not do is quote you an expected survival improvement before we have seen your oxygen data. Anybody who does is quoting somebody else’s farm.