Sudden exposure to warm water causes instant behavioural responses indicative of nociception or pain in Atlantic salmon

• Published in: Veterinary and Animal Science
• Main Authors: Jonatan Nilsson, Lene Moltumyr, Angelico Madaro, Tore Sigmund Kristiansen, Siri Kristine Gåsnes, Cecilie Marie Mejdell, Kristine Gismervik, Lars Helge Stien
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2019
• Subjects: Veterinary medicine; SF600-1100; Atlantic salmon
• Online Access: https://doi.org/10.1016/j.vas.2019.100076; https://doaj.org/article/fc696b2dd3c84869ae47b7479683bdfe

Thermal treatment has become the most used delousing method in salmonid aquaculture. However, concerns have been raised about it being painful for the fish. We studied the behavioural response of Atlantic salmon acclimated to 8 °C when transferred to temperatures in the range 0–38 °C. Exposure time was 5 min or until they reached the endpoint of losing equilibrium and laying on their side, a sign of imminent death. At temperatures below 28 °C, none of the fish reached endpoint within the 5-min maximum. At 28 °C four of five fish reached endpoint, and fish reached endpoint more rapidly as temperature increased further. Fish transferred to temperatures above 28 °C had higher swimming speed immediately after transfer and maintained a high swimming speed until just before loss of equilibrium. Their behaviour was from the start characterised by collisions into tank walls and head shaking. Just before loss of equilibrium they started breaking the surface of the water, swimming in a circle pattern and in some instances displayed a side-wise bending of their body. In other words, salmon transferred to temperatures above 28 °C showed instant behavioural responses indicative of nociception or pain. Keywords: Behavioural response, Fish, Heated water, Nociception, Pain, Thermal delousing