Welfare challenges during Atlantic salmon smolt production and the physiological transition from freshwater to seawater in commercial aquaculture.
Smolt welfare establishes the baseline health and stress capacity that carries forward throughout the sea phase production. Poor welfare during smolt production — inadequate nutrition, high disease burden, crowded conditions, or inadequate physiological preparation for seawater — creates a welfare deficit that cannot be fully compensated later. The physiological sensitivity of smolts during the transformation period means that stressors during this window have disproportionate effects compared to equivalent stressors at other life stages. Welfare-positive smolt production involves optimal water quality, careful management of crowding during procedures, optimal nutrition to support immune function and growth, and careful timing of seawater transfer to align with genuine physiological readiness rather than production scheduling convenience.