Tank- and cage-farmed Atlantic salmon display similar swimming performance and appetite recovery despite differences in gill and heart morphology

Understanding Atlantic salmon physiology is essential for ensuring welfare in aquaculture. Many physiological studies used to establish welfare standards have relied on fish reared in controlled tank settings, yet commercial production occurs in more variable sea cage environments. This raises the question of whether tank-reared salmon serve as reliable models for performance and health assessments of sea cage-reared populations. We compared swimming performance, stress recovery, and morphology between two groups of farmed Atlantic salmon: one reared entirely in tanks and another transferred to sea cages at ~100 g, where they remained for 8 months. Both groups displayed comparable swimming performances and similarly high motivation to feed after 1 week following exhaustive exercise, with no post-exercise mortality observed. However, sea cage-reared salmon had a slower trajectory to recover their appetite and worse snout and skin welfare, suggesting more challenging recovery conditions at sea. Morphological analysis revealed potential trade-offs in gill and heart health: tank-reared salmon had signs of healthier gills but a higher incidence of deviating heart morphology. Unexpectedly, salmon with rounder heart ventricles and more obtuse ventricular bulbus angles swam faster relative to their body size, challenging previous findings and underscoring the need for further investigation into the functional significance of heart morphology. Our results highlight the resilience of sea cage-reared salmon and affirm the role of laboratory tank studies in aquaculture research, especially when complemented by site-specific assessments to bridge experimental and commercial contexts. • Swimming performance was comparable between tank- and cage-reared salmon. • Both groups displayed robust appetite recovery within a week of exhaustive exercise. • Tank-reared salmon had healthier gills but more deviating heart morphologies. • Salmon with rounder hearts swam faster relative to body size, challenging predictions. • Combining tank and cage trials strengthens aquaculture research and its application.