Net pen aquaculture for finfish represents the dominant production system globally. Net pen welfare outcomes depend critically on stocking density, environmental management, and disease control.
Net pen welfare is fundamentally constrained by the density of animals in a finite space. Fish in high-density pens show chronic crowding stress, increased aggression, and suppressed immune function. Poor pen placement in areas with insufficient water flow worsens oxygen depletion and waste accumulation. Welfare-positive net pen management includes appropriate stocking density, strategic pen placement and fallowing rotation, and proactive disease management that reduces treatment need. Moving toward lower-density systems is the most direct welfare improvement available.