Rainbow trout are among the most commonly farmed fish species globally, and their welfare in aquaculture is affected by stocking density, water quality, handling, and slaughter methods that vary widely across operations.
Trout welfare in aquaculture involves chronic stresses from confinement and acute welfare impacts at slaughter. At high stocking densities, subordinate fish cannot access optimal feeding positions, sustain fin damage from contact with conspecifics, and show elevated cortisol reflecting chronic stress. Water quality deterioration causes physiological distress and disease predisposition. Slaughter method is the most acutely welfare-significant variable: ice slurry immersion causes a slow death over minutes in conscious fish that display strong aversion responses; carbon dioxide narcosis is aversive before loss of consciousness. Percussive stunning followed by gill cutting achieves rapid insensibility and is the most humane commercially available method. ASC certification has driven some welfare improvements but the criteria for slaughter welfare remain inadequate in many certified operations. Consumer demand for certified humane slaughter methods creates direct market pressure for improvement.