Smoltification — the physiological transition that prepares salmon for saltwater — is a vulnerable period in aquaculture with significant welfare implications for sea transfer timing and management.
The smolt transfer decision is one of the highest-stakes welfare management choices in salmon aquaculture. Transfer before physiological readiness causes immediate mortality in some fish and chronic osmoregulatory stress in survivors — fish that cannot maintain proper salt-water balance experience a form of systemic physiological failure that impairs every biological function. The commercial pressure to transfer smolts to sea cages according to production schedules rather than biological readiness is a direct welfare risk. Seawater challenge testing provides objective readiness assessment, but its implementation and interpretation require expertise. Welfare regulation that requires documented smolt quality assessment before sea transfer would provide a systematic protection against schedule-driven premature transfer.