How the physiological transformation from freshwater parr to saltwater smolt creates welfare vulnerabilities in both wild and farmed salmon.
Salmon smoltification represents a period of extreme physiological vulnerability during which welfare problems have particularly severe consequences. The smolt's body is committed to a massive physiological transformation, and any additional stressor — including handling, crowding, or poor water quality — during this critical window compromises the transformation and the fish's subsequent survival and health. In farmed salmon, the sea transfer process — which must occur when smolts are physiologically ready — is a significant welfare event that, managed poorly, causes high mortality and chronic stress. Understanding and respecting the timing and fragility of smoltification is essential for welfare-conscious salmon farming.