Smoltification is the physiological transformation that prepares juvenile salmon for saltwater life. In aquaculture, managing this transition poorly causes significant welfare harm and production losses.
Salmon transferred to seawater before completing smoltification experience osmotic stress as their bodies struggle to regulate salt and water balance. This physiological challenge suppresses immune function, increasing vulnerability to sea lice, bacterial infections, and other pathogens. The welfare harm is compounded by the subsequent disease burden and necessary treatments. Best-practice aquaculture uses validated gill scoring, light manipulation, and readiness indicators to ensure fish are physiologically prepared before seawater transfer, minimising this preventable stress event.