Live Fish Transport — Stable Oxygen All the Way

Why transport is critical

Everything about a transport tank works against you at once. The volume is fixed, the biomass density is far higher than in a pen or a RAS hall, and the biological support you normally rely on is not there. There is no biofilter, no settled nitrifying population, and often no meaningful reserve if a parameter starts to drift an hour into a six-hour run.

Four things move at the same time, and they are not independent:

• Oxygen demand rises exactly when supply is hardest. Handling, crowding and pumping raise metabolic rate, and warmer water holds less oxygen while the fish need more of it.
• Ammonia accumulates. Excreted continuously, with nothing to convert it. The proportion present as the toxic un-ionised form climbs with both temperature and pH.
• Carbon dioxide builds up, pushing pH down and adding respiratory load on top of the oxygen problem.
• Stress compounds. Crowding, pumping and confinement are stressors before the boat has left, and stressed fish consume more oxygen — which is the loop that turns a marginal crossing into a bad one.

This applies whether you are moving smolt out to sea, running a well boat between sites, or trucking fish in tanks. What differs is the duration and how much you can intervene mid-route. The parameter everyone watches is dissolved oxygen, because it is the one that kills fastest — but it is also the one most often held by brute force, with more gas pushed in than is actually absorbed.

Nanobubble oxygenation

Conventional oxygenation puts gas into water as comparatively coarse bubbles. Coarse bubbles rise, reach the surface and vent, so a meaningful share of the oxygen leaves the tank without ever dissolving. Operators compensate by increasing the flow, which costs more gas and still leaves gradients: a well-oxygenated layer where the diffusers are, and poorer water elsewhere that the fish avoid by crowding into the good part of the tank.

Nanobubbles behave differently for one reason. Below roughly 200 nanometres, buoyancy barely acts on a bubble, so it does not rise and vent — it stays suspended and drifts with the water, and the gas inside it has time to dissolve. The combined surface area for a given quantity of gas is very large, which is what makes the transfer efficient rather than merely different. The physics is set out on oxygen transfer with nanobubbles.

For wellboat oxygenation that has two consequences worth more than the theory. Oxygen that dissolves instead of escaping is oxygen you paid for and kept, so the same gas consumption holds a higher and steadier level. And a suspended bubble population distributes more evenly through the water column than a rising plume, which reduces the gradients that make fish crowd — and crowding is itself a stressor.

Honest limit: this is a gas transfer technology, not a life-support system. It does not remove ammonia, it does not replace flow-through exchange or planning the route, and it does not compensate for loading a tank beyond what the water can carry.

Less ammonia and stress

Nanobubble treatment does not strip ammonia out of the water, and it would be dishonest to imply otherwise. What it does is act on the part of the problem you can influence in a closed tank.

Ammonia toxicity is a function of concentration, temperature and pH, and it is made materially worse by low oxygen. Fish held at inadequate or fluctuating stable oxygen levels are already under respiratory load, which reduces their tolerance to the ammonia that is accumulating around them. Holding oxygen steady does not lower the ammonia figure on your meter, but it substantially changes how well the fish handle it — and it removes the second stressor that would otherwise be stacking on the first.

Efficient oxidation also works on the dissolved organic load — mucus, faeces, feed residue — that builds through a run and drives oxygen demand upward on its own. Less accumulated organic material means a smaller share of your oxygen going into breaking it down instead of into the fish.

Higher delivery success

Survival at the receiving end is the number that gets counted, but it is not the only outcome that matters commercially. Fish delivered in poor condition recover appetite more slowly, and a slow start after transfer shows up in the growth figures weeks later. Delayed mortality after an apparently successful delivery is a familiar pattern on any site, and it usually traces back to conditions during the run rather than to anything that happened after unloading.

Fish transport water quality is therefore worth measuring properly rather than assuming. Log oxygen at more than one depth, log temperature and pH, and record what actually happened at loading, because that is where most of the stress is applied. Without a baseline from your own crossings on your own routes, neither we nor anyone else can tell you what a change is worth.

• Steadier oxygen through the run, rather than a good average with poor troughs at the worst moments.
• More even distribution through the water column, so the fish are not crowding into one part of the tank.
• Lower gas consumption for the same level, because more of the gas dissolves instead of venting.
• A better starting point after transfer, which is where the delayed losses are avoided.

Biosecurity

Biosecurity in aquaculture water treatment is a regulated regime, not a product. In Norway that means the rules for transporting aquaculture animals administered by the Norwegian Food Safety Authority, route and valve management through sensitive areas, treatment of transport water where it is required, cleaning and disinfection between trips, and documentation of all of it. That framework exists whatever equipment is on board.

Where oxidation contributes on a wellboat is in disinfecting the wells, piping and associated equipment between assignments. NanoOzone Transfer Water delivers ozone as nanobubbles — rated to 300 m³/h in SS 316L with doses up to 5 mg/L — and on a wellboat it is intended for planned disinfection after unloading and before the next loading, not for treating water with fish on board. Ozone oxidises strongly and then reverts to oxygen without a lasting by-product; any residual ozone is destroyed before the water is discharged.

What it is not is a substitute for the regime. It does not exempt a vessel from route requirements, it does not replace cleaning and disinfection procedures, and it does not remove the obligation to document what was done. Treat efficient oxidation as one component in a biosecurity plan that a fish health professional has signed off on.

Reference: 28% higher survival

The one survival figure NanoSWIM publishes comes from an Atlantic salmon producer: survival 28% higher after nanobubble oxygenation was installed, alongside a 40% increase in dissolved oxygen. The full write-up, including the caveats, is on reference: 28% higher survival.

Two things about that reference should be said plainly. The client is anonymised, because we do not have permission to name them — which is a real limit on what it proves. And it is a facility installation rather than a wellboat crossing, so read it as strong evidence for the mechanism, oxygen transfer efficiency, rather than as a measured result from a transport run. If you need transport-specific evidence before a capital decision, ask us for a reference conversation with someone operating comparable routes. An hour with an operator is worth more than any page a supplier writes.

The published field results on this site are the ones above and 85% less chlorine at a resort pool; the wellboat system figures further down are design basis, not results. We do not have transport survival data from your species, your route or your season, and we will not manufacture it.

Wellboat oxygenation and disinfection: two dedicated systems

For wellboats, NanoSWIM has two dedicated marine systems, and they do two different jobs on the same vessel. One adds oxygen while the fish are on board. The other disinfects the empty wells, piping and associated equipment between assignments. Keep the two apart when you specify: neither does the other's job.

• ABAN-20 — oxygen during transport. A skid-mounted module with 20 passive, hydrodynamic nanobubble generators; no electrical power is used inside the generators to make the bubbles. It treats a sidestream drawn from the recirculation loop by the vessel's own seawater pump, feeds in low-pressure oxygen from the vessel's supply and returns oxygen-rich water to the well. Design basis per module: 1,000 m³/h and 100 kg O₂/h in a 1.5 × 0.6 × 2.0 m stainless-steel frame, with about 1.5–3 kW for controls and instrumentation. One module per well is recommended.
• ARVAND-O3 — disinfection between assignments. A skid-built ozone-nanobubble system for closed-loop disinfection of the wells after unloading and before the next loading. ORP and TRO are monitored and logged against a defined contact time, off-gas goes through an ozone destruct unit, residual ozone is removed before discharge, and gas detection with automatic safety shutdown is part of the design. It is not used with fish on board, and capacity is sized per vessel.

What is not proven yet: both systems are offered through a pilot programme. The ABAN-20 figures are a design basis, and the bubble-size measurements behind it are NanoSWIM internal tests, not results from a vessel in service. Neither system changes the limits set out above — oxygen does not remove ammonia, and disinfection between trips sits inside the biosecurity regime rather than replacing it. Specifications, a worked sizing example and the pilot steps are on the wellboat page.

Equipment, and who you should actually be talking to

Outside a permanent wellboat installation, NanoSWIM Mobile is the unit most often specified: trailer-mounted, quick-connect and rated to 150 m³/h, which makes it practical for temporary installations, trials before a capital decision, and sites where a permanent installation makes no sense. For disinfection of the wells between assignments, the ozone-nanobubble systems described above are the relevant specification.

One thing worth being straight about. NanoSWIM's core business is pools and aquatic facilities; apart from the two wellboat systems above, our industrial and wider aquaculture work runs through our sister company NanoMAR, which shares the core nanobubble technology. Depth in salmon logistics and RAS lives on that side of the business. If your project is primarily an aquaculture project beyond the wellboat systems, we would rather introduce you to the people who do it every day than answer at arm’s length — and the shared technology is exactly why results from one sector are relevant to the other.