The smoltification transition from freshwater to seawater is a welfare-sensitive period for farmed Atlantic salmon. Management during this critical phase affects health and welfare throughout sea phase.
The smoltification transition is one of the most welfare-sensitive periods in the Atlantic salmon life cycle, as physiological systems undergo wholesale reorganization for marine life. Premature transfer before smoltification is complete causes osmoregulatory failure, characterized by failure to regulate internal ion concentrations in sea water — a severely stressful condition with high mortality risk. Transfer stress from handling, crowding, and pump systems compounds the physiological challenge of the transition period. Best welfare practice includes careful smolt quality assessment before transfer, minimizing concurrent stressors, and gradual salinity acclimation where operationally feasible. Welfare monitoring in the weeks following transfer provides early detection of osmoregulatory or health problems that may indicate transfer timing or quality issues.