# Oxygen for aquaculture and fish farming

A 2014 Global Aquaculture Advocate article says that in intensive tank-based fish farms with more than 40 kg of fish per cubic metre, fish and bacteria usually consume oxygen faster than typical aeration equipment can dissolve it, so pure oxygen gas is used. It comes from liquid oxygen, cylinders or on-site PSA and VSA generators.

## Why oxygen limits production

In a 2014 article in the Global Aquaculture Advocate, Thomas M. Losordo writes that in many situations the capacity for adding oxygen to water becomes the first limiting factor in a recirculating system’s carrying capacity. The oxygen required is largely dictated by the feed rate and by how long waste solids remain in the system: as little as 0.3 kg of oxygen per 1.0 kg of feed with non-submerged biofilters and quick removal of solids, and as much as 1.0 kg per 1.0 kg of feed with submerged biological filters and retained solids. Depending on the species, dissolved oxygen should be kept at 5 mg/L or higher for acceptable growth rates, and in an intensively loaded system a failure of aeration or oxygenation can lead to a total loss of the fish crop in 30 minutes or less unless backup oxygen or aeration is provided.

## Aeration or pure oxygen

Losordo distinguishes aeration, the dissolution of oxygen from the atmosphere into water, from oxygenation, the transfer of pure oxygen gas into water. With aeration alone, fish density is typically limited to 30 to 40 kg per cubic metre of tank volume; above 40 kg/m³, oxygen consumption by fish and bacteria usually exceeds what typical aeration equipment can dissolve. Pure oxygen gas raises the saturation concentration of oxygen in water nearly fivefold at standard atmospheric pressure. Properly designed oxygen-diffusion devices can absorb more than 90 percent of the oxygen applied, while in shallow tanks even flat-plate diffusers absorb no more than 40 percent; he names down-flow bubble contactors (oxygen cones), pressurised packed columns and low-head oxygenators as efficient options.

## Where the oxygen comes from

Losordo lists compressed oxygen cylinders, liquid oxygen and on-site oxygen generators, and says that in most applications the choice is between bulk liquid oxygen and a generator. The selection should consider the cost of liquid oxygen, which usually depends on the distance from the production plant, and the reliability of the electrical service a generator needs. A 2008 article in the same magazine by engineer Philip Nickerson adds:

- Compressed-oxygen cylinders are too expensive at a commercial scale; if liquid oxygen is not available, compressed oxygen can back up an oxygen generation system.
- Liquid oxygen is normally trucked in and stored in a bulk tank; it does not require electricity, is delivered by its own pressure and is up to 99.9 percent pure.
- VSA and PSA are the two common generation processes: PSA compresses air to 100 to 120 psi, VSA works at 10 psi or lower and needs no air drier, and Nickerson reports that VSA uses less power than a PSA unit producing the same amount of oxygen.
- Generation is not necessarily cheaper than liquid oxygen: late-summer use can be more than twice winter use, and a generator sized for maximum consumption could cost much more than buying liquid oxygen. Liquid oxygen can automatically back up a generator if power is lost, and the most economical option is probably a combination of the two.

## ULTRAOX VSA

The ULTRAOX VSA datasheet lists aquaculture among the applications of this Ultra Controlo industrial oxygen plant. ULTRAOX VSA delivers 75% to 95% oxygen at 50 kPa, with an additional oxygen booster for higher pressures supplied on demand. Its datasheet describes a totally oil-free production system, a skid or container installation and the option to replace cryogenic systems with liquid oxygen tanks or work as the main source of supply. Its seven models deliver 18 to 240 m³/h at 93% oxygen. ULTRAOX VSA is an industrial line, not a medical oxygen plant.

### What dissolved oxygen level do farmed fish need?

It depends on the species. Losordo (2014) gives 5 mg/L or higher as the level for acceptable fish growth rates.

### Is an oxygen generator cheaper than liquid oxygen?

Not necessarily. Nickerson (2008) notes that a generator sized for maximum consumption could cost much more than buying liquid oxygen, and that a combination of the two is probably the most economical option.

## Sources

- [T. M. Losordo, A look at aeration, oxygenation, Global Aquaculture Advocate (March/April 2014), Global Seafood Alliance](https://www.globalseafood.org/advocate/look-at-unit-processes-in-ras-systems/)
- [P. Nickerson, Oxygen sources for aquaculture farms, Global Aquaculture Advocate (July/August 2008), Global Seafood Alliance](https://www.globalseafood.org/advocate/oxygen-sources-aquaculture-farms/)
- [ULTRAOX VSA datasheet, p. 2 and p. 3](https://www.ultracontrolo.com/products/ultraox-vsa)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/industry/oxygen-for-aquaculture/