Chronic turbulence and Atlantic salmon (Salmo salar): assessing effects on growth performance, behaviour, welfare, stress and swimming capacity.

An increasing number of aquaculture companies aim to relocate Atlantic salmon (Salmo salar) farms to offshore locations exposed to large wave action. However, the impact that this environment will have on the fish reared within remains unknown, raising questions about their coping ability and welfare. The purpose of this study was to address this knowledge gap and understand how Atlantic salmon respond to wave-induced turbulence. For 8 weeks, post-smolts were exposed to chronic turbulence created using specially designed wave-generating equipment. During the trial, growth, behavioural conditioning, plasma biochemistry and welfare were monitored. At the end of the study, swimming capacities were determined, and vertebral deformities were analysed in a sub-group of fish. Despite both control and turbulence groups doubling their weights, the turbulence group exhibited a 5% reduction in size. A dropin appetite, 17% across the first five days, and deviant behaviour was observed for the first 3 weeks in the turbulence group. These disparities disappeared in the latter half of the trial, suggesting the fish acclimatized. Welfare scores, haematological parameters, critical swimming speeds and deformity prevalence remained similar across both groups, suggesting the fish were not impacted by chronic turbulence on a physical or physiological level. This was the first attempt at experimentally studying the effect of constant turbulence on a cultured species, providing valuable insights for establishing responsible offshore aquaculture practices. Our findings clearly demonstrate that Atlantic salmon is a robust species with the capacity to adapt to novel high-energy environments without suffering substantial reductions in welfare or longterm production performance.