FARMED SALMON ARE STRESSED BY NOISE

Farmed salmon are stressed by noise. Very loud noise over time can cause chronic brain stress in farmed salmon, but they cope well with most sounds in fish farms.

Author: Øystein Rygg Haanæs

The Institute of Marine Research has previously shown that farmed salmon live in a noisy world .

Now, researchers at HI, NMBU and Deakin University have looked at how noise affects farmed salmon.

“Salmon that were exposed to loud, stressful noise for five minutes a day for 30 days reacted with a flight response and increased production of the stress hormone cortisol,” says HI researcher Frode Oppedal.

The sound level in the experiment corresponds to what salmon can experience in farming in connection with very noisy work, hatches being slammed shut or nearby blasting. 

Proposes more noise reduction measures

In a recent research report, HI presents several recommendations for reducing noise in fish farms.

“This includes obvious measures such as reducing unpredictable noise where possible, such as installing dampers on hatches. Blasting work nearby should be avoided, or the sound should at least be dampened with bubble curtains,” says Oppedal.

The researcher also points out that electric boats make less noise than motor-powered ones, and that fish farms should preferably not be located where there is constant, noisy boat traffic.

Signs of chronic brain stress

Over time, fewer fish responded to the sound, and the production of the stress hormone cortisol decreased.

“This means that the salmon gradually got used to the familiar sound that was repeated daily. After a month, we still saw signs of chronic stress in the brain,” says Oppedal. 

Gene expression that is normally positively associated with growth and reproduction was also inhibited.

Can salmon be prepared for noise in the sea?

The life cycle of farmed salmon begins in freshwater before being released into saltwater.

To find out if the salmon can be prepared for the noise that awaits in the cages, experiments were conducted in which salmon smolts in freshwater tanks were exposed to different types of noise.

One group of smolts was exposed to unpredictable sounds from fish farms, while another was exposed to predictable sounds from such facilities. A control group experienced the normal soundscape in the fish farm tank.

“We found no differences between the tank groups in the freshwater phase and no reactions that indicate that sound created stress. All also had normal cortisol responses to a standard stress test in which they were confined in a confined environment for 30 minutes. We interpret this as meaning that none of the studied sound environments in the freshwater phase are more or less stressful,” explains Oppedal.

Surprising stress response in the sea

When the salmon were released into the cages, however, the researchers got a surprise.

“Fish that had only experienced the farm’s own sound in freshwater reacted with smaller changes in behaviour when exposed to sound in the cage. While both behaviour and neurochemical responses showed that fish that had experienced predictable sound from the farm in the freshwater phase were more stressed by sound in the sea phase,” says Oppedal.

All groups of fish reacted as normal with increased production of cortisol when exposed to additional stress in the sea.

The control group and the group that experienced unpredictable sound in the freshwater phase also reacted with increased production of the neurotransmitter serotonin in the brain when they were further stressed through confinement. The group that had received predictable sound in the freshwater phase did not.

“The fact that cortisol levels increase during stress without serotonin levels increasing can be harmful in that it leads to poorer brain health.” explains Oppedal.

For example, it can lead to lower neuroplasticity. This weakens the brain’s ability to adapt to environmental and behavioural changes by altering the connections between nerves and brain cells.

Research on long-term effects is important

Oppedal believes that it is now important to conduct further research into which frequencies, durations and intensities of sound affect salmon’s behaviour, physiology, appetite, growth and welfare. 

So far, researchers know very little about how salmon are affected by sound at very low frequencies. 

In the sea, sound creates movement in the water, so-called particle movement. At low frequencies, particle movement is both an important part of the sound and difficult to measure. 

“We also need more knowledge about the long-term consequences of the noise experienced by farmed salmon, and how new types of facilities can affect the salmon’s soundscape. A future focus should also be to create more standardised measurement methods for noise in salmon farming, so that the farmers themselves can take measures and measure the effect.” says Oppedal.

Reference:

F. Oppedal et al.: « Noise as a possible stress factor and welfare challenge in the aquaculture industry — Final report FHF #901744 «Soundscape» ». Report from marine research 2025-10.

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