Rainbow trout are one of the most widely farmed fish globally. Improving their welfare requires addressing chronic crowding stress, handling practices, and slaughter methods.
Rainbow trout welfare suffers significantly in high-density commercial systems. Chronic crowding stress suppresses immune function, increases aggression-related injuries, and prevents the expression of natural behaviours including spatial preference and shoaling dynamics at appropriate densities. Handling events — sorting, grading, vaccination, and transport — cause acute stress characterised by elevated cortisol that can persist for hours. Slaughter welfare is particularly problematic: many farms use asphyxiation on ice, which causes prolonged distress before death in a species that retains consciousness for several minutes in cold water. Percussive stunning or electrical stunning before killing dramatically reduces suffering. The Humane Slaughter Association has developed guidance for on-farm trout slaughter that specifies effective stunning methods — implementation remains patchy across the industry.