Crowding, air exposure, and handling before slaughter cause severe physiological stress in salmon; improved crowding protocols and immediate post-crowding slaughter reduce welfare impacts.
The pre-slaughter period for farmed salmon involves a cascade of stressors that begins with crowding using a purse net, continues through air exposure during transfer, and ends with the slaughter event itself. Each step activates the stress response, depleting energy reserves and causing significant physiological disruption. Welfare-progressive slaughter systems attempt to minimize the time between initial crowding and loss of consciousness, reduce air exposure to seconds rather than minutes, and improve the stunning and killing method. These improvements also produce economic benefits through reduced stress-related flesh quality problems.