Fish obtain dissolved oxygen – DO from water through their gills.
Oxygen supports metabolism, digestion, swimming, protein synthesis, immune function and growth.
Low DO may not immediately kill fish, but it can reduce appetite, slow growth, worsen feed conversion and increase stress.
The objective is therefore to maintain a stable DO level that supports optimum production.
As water temperature rises, oxygen solubility decreases.
| Temperature | Approx. O₂ Saturation |
|---|---|
| 10 °C | 11.27 mg/L |
| 20 °C | 9.02 mg/L |
| 25 °C | 8.18 mg/L |
| 30 °C | 7.44 mg/L |
Warm water may hold less oxygen while biological demand increases.
Salinity and altitude also reduce oxygen-holding capacity, so every farm must be evaluated according to actual site conditions.
Trout and salmon generally require high and stable DO levels.
Sea bass and sea bream become increasingly dependent on oxygen management under intensive production.
Tilapia, carp and catfish may tolerate lower DO, but tolerance does not mean optimum growth.
Feed conversion requires metabolic energy:
Feed → Digestion → Metabolism → Protein Synthesis → Growth
Oxygen supports this entire chain.
Demand can also rise after feeding, so oxygen systems must be sized for maximum biomass and peak demand, not only average consumption.
A typical RAS process may include:
Fish Tank → Mechanical Filtration → Biofilter → CO₂ Degassing → Oxygenation → Return
Both fish and biological treatment processes consume oxygen.
High DO does not automatically solve high CO₂, so oxygenation and degassing should be engineered together.
Common technologies include:
The appropriate method depends on flow, pressure, target DO and hydraulic design.
PSA – Pressure Swing Adsorption separates oxygen directly from atmospheric air.
Typical configuration:
Air Compressor → Air Receiver → Filtration and Drying → PSA Oxygen Generator → Oxygen Receiver → Analysis and Control → Oxygenation System
Zeolite molecular sieve adsorbs nitrogen and produces an oxygen-enriched gas stream.
For many aquaculture applications, approximately 90–95% O₂ is suitable.
The key process parameter is not maximum gas purity but the stable DO achieved in the water.
| Criterion | PSA | LOX |
|---|---|---|
| Source | Atmospheric air | External gas plant |
| Production | On site | Off site |
| Tanker dependence | Low | High |
| Electricity | Required | Low on site |
| Cryogenic tank | Not required | Required |
| Logistics dependence | Low | High |
| Expansion | Modular | More storage/deliveries |
| Main OPEX | Electricity + maintenance | Gas + logistics |
For high and continuous oxygen consumption, PSA can be an attractive economic alternative.
However, oxygen is a life-support utility, so redundancy must always be considered.
A common approach is:
PSA = Base Load
LOX = Emergency / Peak Load
Engineering should consider:
Basic hydraulic calculation:
O₂ Requirement (kg/h) = Water Flow (m³/h) × ΔDO (mg/L) / 1000
Actual projects must also include fish respiration, biological demand, peak loads and transfer losses.
Mentis Engineering evaluates aquaculture projects as complete oxygen systems:
Compressed Air + Air Treatment + PSA Oxygen Generation + Oxygen Storage + Analysis + Automation + Oxygen Transfer
The starting point is not the generator model but the actual oxygen demand of the fish and process.
Properly engineered on-site generation can reduce dependence on liquid oxygen deliveries, improve cost predictability and provide greater control over oxygen supply.
Mentis Engineering – On-Site Oxygen Generation for Aquaculture
