Rainbow trout are the most widely farmed freshwater fish in the UK, and disease management - particularly for enteric red mouth disease and furunculosis - is central to welfare outcomes.
Trout disease welfare is fundamentally a management problem: overcrowded, stressed fish in poor water quality are far more susceptible to disease than fish in well-managed conditions. The investment in vaccination programmes has dramatically reduced the need for antibiotic treatment in some disease contexts, improving both welfare (less disease-related suffering) and environmental impact. Welfare certification schemes that set measurable standards for water quality, stocking density, and slaughter method provide a framework for continuous improvement. The gap between certified and non-certified production in welfare outcomes can be large.