Recirculating aquaculture systems (RAS) offer potential welfare improvements over open net pens for farmed trout, but introduce new challenges including water quality management, handling stress, and stocking density.
RAS trout farming offers genuine welfare improvements in some dimensions while creating new challenges in others. Eliminating sea lice removes a significant chronic welfare burden experienced by open net pen fish. Consistent water quality and temperature reduce environmental stress. However, high stocking densities still possible in RAS exceed what wild trout would experience, causing chronic stress and fin damage. The frequent handling inherent in RAS management — grading by size, health inspections, transfers — causes repeated acute stress events with cumulative welfare impacts. Biosecurity protocols mean disease spread is controlled but treatment involves mass medication. The closed environment means fish cannot express normal ranging behaviour. Overall, well-managed RAS represents a welfare improvement over many conventional systems, but is not inherently high-welfare without careful density and handling management.