Tolerance limits to fluctuating water currents in Atlantic salmon (Salmo salar): A novel method to simulate the impact of ocean waves on salmon welfare in the laboratory
MetadataShow full item record
- Master theses 
The Norwegian aquaculture industry aims to expand the production of Atlantic salmon (Salmo salar) to offshore locations where the fish will be experiencing more extreme weather conditions compared to traditional sheltered farms. Consequently, acceptable welfare guidelines are needed to ensure that the salmon will thrive in these wavy environments. However, studies have yet to test how the fish will perform in a fluctuating water current compared to a steady current. Therefore, with an updated swim tunnel system, the water flow was programmed to alternate between high and low current speeds, simulating big oceanic waves where groups of six Atlantic post-smolt were tested at 9°C. First, the fish group's critical swimming speed (Ucrit) was established (94.5 cm s-1). Then, trials with peak current speeds of 80, 100, 120, and 140% of the group mean Ucrit were conducted for up to four hours or until the fish fatigued. The low current speed interval was set to 20% Ucrit, and wave periods differed between 30, 60, and 120 s. In peak speeds of 80% and 100% Ucrit, all fish endured for four hours, while only an average of three fish completed the tests at 120% Ucrit. At 140% Ucrit, all fish reached fatigue within 1.5 hours (51 ± 19 minutes). The results indicate that salmon can endure a ≈ 20% higher speed in fluctuating water currents compared to established swimming limits from earlier studies with a constant current. Furthermore, fatigue time did not differ significantly between wave periods, suggesting that the current peak speed is more decisive than the wave period. However, the results of the present study primarily represent an upper threshold value for brief periods of extreme conditions conducted in laboratory settings, and further studies should investigate long-term exposure and more complex wave dynamics under natural conditions.