Open net pen aquaculture dominates global fish farming but creates specific welfare challenges related to sea conditions, disease exposure, and environmental complexity.
Net pen aquaculture welfare involves tradeoffs compared to land-based systems. Net pens expose fish to variable natural conditions — which can provide environmental complexity — but also to disease and parasite pressure from wild populations. Pen depth affects fish ability to select preferred light and temperature conditions by diving. Large, deep pens with moderate currents allow more natural swimming behavior than shallow, overcrowded pens. Disease management in open systems requires pharmaceutical interventions that have their own welfare implications. The comparison between net pen and recirculating aquaculture systems is complex from a welfare perspective, as each system type presents different challenges. Standards specific to net pen conditions are developing as welfare science advances.