Scientists have discovered how salmon "swear" when they're cramped

Scientists do not yet know how exactly fish make these clicks. Among the versions are the movement of the jaw, the release of air or processes related to the intestines.

Details

Atlantic salmon is not generally considered a "talkative" fish. Unlike some species, such as cod, it is not known for active sonic communication. So the clicks that appeared during a stressful situation came as a surprise to the researchers.

One of the experiments used small sea cages with about 40 fish in each. The scientists gradually raised the bottom of the cage, reducing the available water volume. This created crowding, a situation that is considered stressful for salmon.

Sounds were recorded using hydrophones - underwater microphones. The automatic detection algorithm showed a dramatic increase in acoustic events during crowding: up to 1,000 events in 10 minutes versus about 20 events in 10 minutes the day after the stressful procedure.

The researchers also correlated the acoustic events with activity and heart rate data from the fish. This showed that passive acoustic monitoring could be a promising way to track stress in farmed salmon.

Separately, the SINTEF team studied the noise environment in real marine cages. In the 2026 paper, a hydrophone recorded sounds in an open cage from July to November 2023, and the researchers compared normal conditions, fish handling and net cleaning. This is important because aquaculture is not a quiet environment: noise is created by waves, wind, vessels, equipment and farm operations.

Why it matters

For fish farming, it's not just a curious detail. Stress in salmon can impair fish welfare, increase the risk of injury and complicate farm operations. Aggregation is particularly important because it is used when moving fish between cages or before treatments.

Nowadays, the condition of fish is often assessed visually by looking at behaviour, activity at the surface and group density. But when the fish are deeper or there are many of them, such monitoring is limited. Underwater microphones can provide an additional way of monitoring without touching the fish or interfering with their environment.

It is important not to exaggerate: clicks do not mean that salmon are "screaming in pain" or consciously complaining. For now, it's more correct to say that scientists have discovered an acoustic sign related to stress crowding.

Background

Passive acoustic monitoring is a technique in which researchers do not send a signal into the water, but simply "listen" to the environment using hydrophones. This is a way to study marine animal behaviour, sound background and the effects of human noise. NOAA describes such technologies as a way to observe the behaviour and movements of marine animals and assess how they are affected by anthropogenic noise.

In the case of salmon, the direction is still evolving. Researchers have previously observed that sound patterns change when fish are hungry or frightened, but interpreting these signals has remained challenging. The challenge now is to understand which sounds are associated with stress, how they arise and whether they can be used in real time on fish farms.

Source

The main findings are a study by Kristbjörg Edda Jónsdóttir et al. Detection of a stress-related acoustic signature by passive acoustic monitoring in Atlantic salmon farming, published in Aquacultural Engineering in 2024, and a paper on long-term underwater passive acoustic monitoring of the soundscape in an Atlantic salmon sea cage, published in Aquaculture International in 2026. They studied Atlantic salmon sound signalling and the noise environment of sea cages.