Tolerance to fluctuating currents in farmed Atlantic salmon: a novel method to simulate offshore wave effects in the laboratory

Abstract

To ensure acceptable animal welfare in emerging offshore Atlantic salmon aquaculture, it is crucial to understand the biological limits of the fish. Much work has been done on the effects of water currents, but few studies exist on waves, owing to logistical limitations. The purpose of this study was therefore to establish a method to replicate wave-like fluctuating water currents in the laboratory and quantify tolerance limits in salmon. To accomplish this, a swim tunnel system was modified so that current speeds could be programmed to automatically alternate between minimum and peak speeds of a desired magnitude and interval. The critical swimming speed (Ucrit) was subsequently measured in salmon of ~800 g as a baseline from which standardized tests of fluctuating currents could be prescribed. Fluctuating current trials were then performed using minimum speeds of 20% Ucrit and peak speeds of 80, 100, 120, and 140% Ucrit, and cycles of 0.5, 1, and 2 min. Fish were tested for 4 h or until they fatigued. All fish at 80 and 100% Ucrit endured 4 h of fluctuating currents. However, at 120% Ucrit, only 17% completed the test, and at 140% Ucrit, all fish became fatigued within 1.5 h, thus defining acute limits to fluctuating peak speeds. Wave interval did not affect fatigue times significantly. In conclusion, a novel method is introduced here to assess tolerances to various wave-like environments, showing that salmon can endure ~20% higher peak speeds in dynamic fluctuating currents when compared to known swimming capacities at constant speeds.