# Dissolved Oxygen in Aquaculture: What Level, and Why Does It Drop?

> What mg/L of dissolved oxygen fish farming needs, why it drops, when to measure it and what to do when it falls. Aeration calculation and monitoring guide.

- URL: https://demo.fcrsoft.com/en/aquaculture/dissolved-oxygen-in-aquaculture
- Language: en
- Updated: 2026-10-03
- Publisher: FCRSOFT (https://fcrsoft.com)

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# Managing Dissolved Oxygen in Aquaculture

Dissolved oxygen is the most critical water quality parameter for survival, appetite and feed use. When oxygen falls, appetite and FCR suffer first, then health.
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## What level in mg/L?

Keep it above 5 mg/L for most warm-water species and above 6–7 mg/L for cold-water species like trout and salmon. Below 3 mg/L can be lethal for many species.
[Free tool Water Quality Checker](https://demo.fcrsoft.com/en/tools/water-quality-checker)

## Why does oxygen drop?

- High water temperature: warm water holds less oxygen.

- High biomass and increased consumption after feeding.

- Photosynthesis stops at night: the lowest values appear towards dawn.

- Days when currents weaken or the water stratifies.

**Monitor Water Quality 24/7**Oxygen, temperature and pH readings are recorded per cage; sensor data is collected automatically and you are alerted when thresholds are exceeded.
[Open the live demo](https://demo.fcrsoft.com/login.php?package=farm) [Net-Pen Farming Software](https://demo.fcrsoft.com/en/solutions/net-pen-fish-farming-software)

## When should it be measured?

The most critical reading is taken just before sunrise. In warm periods measure at least twice a day, ideally continuously with a sensor.

## What to do when oxygen falls

- Reduce or stop feeding immediately.

- Increase aeration or oxygen supplementation.

- Postpone stressful operations such as grading or net changes.

[Free tool Oxygen Demand and Aeration Calculator](https://demo.fcrsoft.com/en/tools/oxygen-demand-calculator) FCRSOFT

## FCRSOFT does this for you automatically

You don’t need to do the calculations and checks on this page by hand every day. FCRSOFT derives them all automatically from the records entered in the field.

- Oxygen, temperature and pH readings are recorded per cage.

- Sensor data is collected automatically, with instant alerts when thresholds are crossed.

- Water quality history is reviewed side by side with FCR and mortality data.

[Open the live demo](https://demo.fcrsoft.com/login.php?package=farm) [Explore the Farm package](https://demo.fcrsoft.com/demo/farm?hl=en)

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Last updated: 10/3/2026

## Related tools and guides

[Free tool ### Oxygen Demand and Aeration Calculator From biomass and oxygen consumption rate, calculate hourly and daily oxygen demand and the number of aerators needed. Open the tool](https://demo.fcrsoft.com/en/tools/oxygen-demand-calculator) [Free tool ### Water Quality Checker Choose your species and enter temperature, dissolved oxygen, pH, ammonia, nitrite and salinity to see a good, caution or critical status for each parameter. Open the tool](https://demo.fcrsoft.com/en/tools/water-quality-checker) [Guide ### Managing Ammonia and Nitrite What are total ammonia (TAN), free ammonia (NH₃) and nitrite, which levels are dangerous and how to lower them? How pH and temperature affect ammonia toxicity. Read the guide](https://demo.fcrsoft.com/en/aquaculture/ammonia-and-nitrite-in-fish-farming) [Guide ### What Should Stocking Density Be? How is stocking density (kg/m³) set in cages, ponds and RAS? The effect of high density on FCR, growth and mortality, and the right stocking calculation. Read the guide](https://demo.fcrsoft.com/en/aquaculture/fish-stocking-density)