The transfer of Atlantic salmon smolts from freshwater hatcheries to sea cages is a high-risk welfare event that causes significant physiological stress, with mortality and long-term health effects that welfare-focused protocols can reduce.
Smolt transfer is one of the highest-stress events in the salmon production cycle. The physiological sensitivity of smoltification means that handling stress at this stage has disproportionate welfare and health consequences. Cortisol elevation during transfer suppresses immune function, making fish more susceptible to disease for weeks afterward. Oxygen depletion in crowded transfer tanks or pipes causes acute hypoxic stress. Best practice protocols - careful timing of transfer within the smoltification window, maintaining dissolved oxygen levels, minimizing crowding time, and rapid adaptation to salinity - can significantly reduce welfare impacts and improve subsequent health outcomes.