Marine Aquaculture Water Quality Monitoring Case

Marine cage farms face a monitoring problem that surface measurements alone may miss: dissolved oxygen can vary significantly with water depth.

At a large yellow croaker farm in Ningde, Fujian, traditional monitoring relied heavily on operator experience. This made it difficult to continuously identify changes in dissolved oxygen and temperature near the bottom of the cages, where low-oxygen conditions could develop before they were visible at the surface.

The project therefore focused on one practical control chain:

Water Stratification → Multi-Depth Monitoring → Low-DO Warning → Aeration Response → Aquaculture Risk Control

The Problem: Bottom-Water Hypoxia Is Easy to Miss

Temperature affects water density and stratification as well as dissolved oxygen conditions, so measurements taken at only one depth may not fully represent the water conditions experienced throughout a marine cage.

For the Ningde farm, this was the central problem.

Periodic manual checks could show water quality at the time and depth of sampling, but they could not continuously track how DO and temperature changed from the surface to the bottom of the cage.

For high-density yellow croaker farming, delayed detection of bottom-water hypoxia could mean delayed aeration and increased production risk.

Multi-Depth DO Monitoring Instead of One-Point Measurement

To address this problem, the project deployed 8 sets of sensors at key locations in the aquaculture area.

The sensors monitored:

Dissolved Oxygen + Temperature

at different depths from the surface to the bottom layer, allowing operators to observe vertical changes instead of relying on a single measurement point.

The system was designed around:

Surface DO / Temperature
↓
Mid-Water DO / Temperature
↓
Bottom DO / Temperature
↓
Identify Stratification & Low-DO Conditions

This is the key technical difference in the project.

The objective was not simply to collect more measurements. It was to identify whether oxygen conditions near the bottom were deteriorating while conditions closer to the surface remained less affected.

APURE dissolved oxygen monitoring can also be used as an operating input for aquaculture aeration control.

From Low-DO Detection to Aeration Response

The monitoring nodes used equipment designed for continuous marine deployment, with attention to corrosion resistance and biological fouling under seawater conditions.

Measurement data was transmitted wirelessly to a cloud platform, allowing operators to check current conditions and trends remotely.

More importantly, the system converted monitoring data into an operational response:

Bottom DO Drops
→ Threshold Alert
→ Operator Notification
→ Aeration Response
→ Reduced Hypoxia Risk

According to the project record, the system successfully provided early warnings for multiple bottom-water hypoxia events associated with hot and stagnant weather conditions. Operators could respond before the events developed into more serious aquaculture losses.

The project also reported improved fish survival and reduced dependence on experience-based management, although the supplied project record does not provide a numerical survival-rate improvement. For this reason, no percentage is assigned here.

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