Researchers examine noise stress in farmed salmon.
A new study by the Institute of Marine Research (HI), Norwegian University of Life Sciences (NMBU), and Deakin University has investigated the impact of noise on farmed salmon, revealing potential long-term stress effects on brain function.
Farmed salmon live in a noisy environment, with sounds from equipment, boat traffic, and operational procedures creating a constant backdrop in aquaculture facilities. While salmon generally tolerate much of this ambient noise, extreme sound levels, such as those from blasting or heavy equipment use, can trigger stress responses.
“Salmon that were exposed to loud, stressful noise for five minutes a day over a 30-day period exhibited a flight response and increased production of the stress hormone cortisol,” said HI researcher Frode Oppedal. The sound levels used in the study reflected the conditions salmon might experience in farming environments where sudden loud noises occur, such as hatch doors slamming or nearby blasting.
Over time, fish exposed to repetitive noise began to show signs of habituation, with a reduction in their initial stress response. However, researchers also found indicators of chronic brain stress, with suppressed gene expression linked to growth and reproduction. This suggests that while the salmon adapted to the noise, the long-term physiological impact could still be detrimental.
The study recommends measures to reduce excessive noise in farming operations, such as installing dampers on equipment, limiting blasting near facilities, and transitioning to quieter electric boats. Researchers also highlight the need to avoid placing fish farms in areas with heavy boat traffic.
Experiments were also conducted to determine whether exposing salmon to noise in their freshwater rearing phase could help them adapt to the conditions they would later face in the sea. Smolts in freshwater tanks were exposed to both predictable and unpredictable sounds from fish farms, while a control group experienced only the natural sound environment of the tanks.
“We found no significant differences between the groups in the freshwater phase, and all showed normal cortisol responses when subjected to a standard stress test,” Oppedal said. However, when the salmon were later transferred to sea cages, researchers observed unexpected results. Fish that had been exposed only to farm-generated sounds in freshwater exhibited smaller behavioral changes when faced with noise in the sea. Meanwhile, those that had experienced predictable farm noises in freshwater showed a stronger stress response once in the cages.
“All groups of fish reacted as expected with increased cortisol production under stress, but only the control group and those exposed to unpredictable noise in freshwater also showed a rise in serotonin levels,” Oppedal explained. “For the fish that had experienced predictable noise, serotonin did not increase, which could indicate a negative impact on brain health.”
Lower serotonin production in response to stress is associated with reduced neuroplasticity—the brain’s ability to adapt to environmental changes by forming new neural connections. This could make salmon less resilient to external pressures in farming environments.
Oppedal emphasizes the need for further research into the long-term effects of noise on salmon welfare. “We still know little about how very low-frequency sounds affect salmon behavior and physiology. In the sea, sound moves water particles, creating particle motion that is difficult to measure but plays a key role in how fish perceive their environment,” he said.
Future research should focus on standardized noise measurement methods to allow farmers to assess and mitigate noise impacts in aquaculture facilities. “Understanding how soundscapes influence farmed salmon will be critical as the industry evolves, particularly with the development of new production systems,” Oppedal added.
