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Salmon make clicking sounds when stressed – but no one knows how they do it
Salmon usually go about their lives quietly, unless they are stressed. Their clicking sound is so unusual that researchers don’t even know if they make the sound with their heads or their rear end.
Published
It’s noisy underwater. Especially just below the surface.
“A lot of the ambient noise is from the wind and waves,” says Kristbjörg Edda Jónsdóttir, a researcher at SINTEF.
She has studied how much noise salmon make during normal net cleaning operations as well as how the same salmon produce strange sounds when they feel crowded.
Stressful when space is cramped
“We had small sea cages with around 40 fish in each. We raised the bottom of the cages bit by bit, so that they had less water volume to move around in,” she says.
Less space is stressful for the salmon.
They are fast swimmers with extreme endurance, and they can swim long distances. They do not thrive when their environment becomes cramped.
A quiet species
“We detected a strange clicking sound when the salmon became stressed,” says Jónsdóttir.
This was particularly surprising because salmon are not actually a talkative – or vocalising – species. Cod, for example, use sound to communicate. But salmon do not talk to each other that way.
The salmon clicking is so unique that the researchers do not even know whether they make the clicks from their head or their rear end.
There has been some research done where sounds were recorded for a couple of days, but this is the first long-term study lasting several months.
Burping or passing gas?
“We aren’t sure what produces the sound. One theory is that the salmon opens its jaw to release air and makes a mechanical sound. Or it could be that it is trying to empty air from its intestinal system," says Jónsdóttir.
She adds that the more cramped things became for them, the more cases of this sound were identified.
Researcher Gaute Alexander Nedberg Helberg has detected a similar acoustic event from salmon in a RAS facility. This is a land-based farm where the water is cleaned and reused.
The clicking arose when the salmon were being fed, which can also be a stressful activity for them.
Noisy housecleaning
Jónsdóttir and her colleagues have now measured how much noise is produced in the net cleaning process – that is, the washing of the sea cages where the salmon live.
“There’s so much noise. It’s incredibly loud. We were aware that it was noisy, but just how noisy hadn’t been documented,” she says.
There have been some earlier studies that recorded the underwater acoustic soundscape for a couple of days, but this is the first long-term monitoring over several months.
"This allowed us to look at the periods with and without net washing, and then we compared them,” the researcher says.
Fish movement during cage cleaning
At its loudest, the sound level reached 139 dB.
On land, this level would be well above the pain threshold for humans, but sounds above and below water are not really comparable.
The researchers cannot say for sure how loud the salmon perceive this level to be.
Wild salmon swim upstream in rivers where the noise level can be even louder in many places.
“One theory holds that farmed salmon have poorer hearing than wild salmon,” says Jónsdóttir.
Other experiments she has done show that the fish move around while the cages are being washed. The researchers lack enough data to determine whether this actually indicates that the cleaning noise causes them to move away.
Limited research available
“Research on sound in aquaculture is still in its early stages. Treatment of salmon is perhaps the most invasive activity that they are exposed to," says Jónsdóttir.
The research has focused much more on making these activities gentle to avoid exposing the fish to things we know can cause direct damage to them.
"Sound has not had the highest priority,” she says.
Underwater acoustic monitoring has been more about the impact of ambient noise from ships on mammals, not farmed fish.
“We may find that noise is no problem at all. But I think there will be more focus on this in the future,” the researcher says.
References:
Helberg, G.A.N. Acoustic characteristics of Atlantic salmon feeding behaviour in RAS: Possibilities and pitfalls of using passive acoustics for monitoring in tanks, Doctoral thesis at UiT The Arctic University of Norway, 2026.
Jónsdóttir et al. Detection of a stress related acoustic signature by passive acoustic monitoring in Atlantic salmon farming, Aquacultural Engineering, 2024. DOI: 10.1016/j.aquaeng.2024.102472
Jónsdóttir et al. Long-term underwater passive acoustic monitoring of the soundscape in an Atlantic salmon sea cage, Aquaculture International, 2026. DOI: 10.1007/s10499-026-02522-1
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