The transition of farmed salmon from freshwater to marine environments — smoltification — is a physiologically critical period with significant welfare implications that management practices must carefully support.
Smoltification represents a period of heightened vulnerability for farmed salmon where physiological demands of transformation combine with the welfare costs of transfer operations. Fish transferred at the wrong stage of smolt development face impaired osmoregulatory function in seawater, causing chronic physiological stress and elevated mortality. The combination of developmental vulnerability, handling stress during transfer operations and immediate exposure to sea lice in open-net pen environments creates a welfare challenge at the entry point to the marine grow-out phase. Welfare-conscious aquaculture management uses smolt quality assessment, optimises transfer timing to the smolt window, minimises handling duration and considers transfer to RAS marine facilities where sea lice exposure can be controlled.