| Summary: | Much is known about the life cycle and growth of the Atlantic salmon, but there has been less focus on the behaviour and neurobiology of these animals in captivity and how they interact with each other and their environment. Salmon in aquaculture rearing tanks are normally kept in confinement in a homogenous environment without any enrichments, which raises both ethical as well as welfare related questions. Therefore, this study aimed to delve into the potential of different commercially applicable enrichments to increase welfare. The study explored the hypothesis that bubbles, increased water current and stones would each contribute to improved welfare by comparison with rearing in unenriched standard rearing tanks (the control treatment), as measured by increased social cohesion, reduced aggression, and increased cell proliferation in the telencephalon. There were 30 salmon randomly distributed in each of 12, 100-litre tanks where 3 of the tanks were Controls, whilst the rest of the tanks were evenly distributed among the enrichments Bubbles, Current and Stones, all followed for 6 weeks. The enrichment treatments used were Bubbles (intermittent release of small air bubbles in the tank), Current (increased current around the wall of the tank), and Stones (structural enrichment with 6 stones at the bottom of the tank). Videos from Control and enriched tanks were made on one day per week over a 6-week period. To assess social cohesion, snapshots were taken at two time points per 15-min video (1 min after the start of the video and 1 min after the start of bubbles in the Bubbles treatment and corresponding time points in the other treatments). From each photograph, distances between the snouts of each individual in a tank were calculated to find the average distance as a measure of social cohesion. Additionally, numbers of aggressive attacks in each tank were counted during two 5-min periods per video (0-5 min at the video start, and 10-15 min at the end of the video). Telencephalon cell proliferation was measured ...
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