Net pen design, size, and stocking density are fundamental determinants of salmon and other finfish welfare in marine cage aquaculture. Getting these parameters right is essential for fish health and welfare.
Net pen design encapsulates the key challenge of marine finfish aquaculture welfare: the fish are confined in a defined volume, and every aspect of that confinement - size, depth, stocking density, water exchange - affects their physical and behavioral welfare. Welfare science has established that salmon in overcrowded pens show elevated stress indicators, higher disease susceptibility, more aggressive behavior, and poorer growth - making density a welfare and commercial concern simultaneously. Progress requires regulatory standards based on welfare evidence rather than production convention, combined with monitoring systems that use fish behavior as the primary welfare indicator. The industry's move toward larger, deeper pens with better water exchange represents genuine progress, but stocking density standards in many regions still lag behind the evidence.