Rainbow trout are among the most intensively farmed fish globally. Their welfare is shaped by crowding, water quality, handling stress, and the adequacy of slaughter methods.
Rainbow trout welfare is shaped by the mismatch between their natural habitat — clear, fast-flowing streams with high oxygen levels — and the intensive sea or land-based cage systems in which most are farmed. Crowding reduces dissolved oxygen, increases waste accumulation, and creates competitive resource stress that causes chronic elevation of cortisol and suppression of immune function. Fin erosion from crowding and abrasive contact is a visible welfare indicator. Individual personality differences in trout — documented through repeated behavioural testing — suggest that different individuals experience the same environment differently, with more anxious individuals potentially suffering more in intensive systems. Humane slaughter using electrical stunning dramatically reduces suffering compared to asphyxiation — the traditional method — and represents an achievable welfare improvement at minimal cost.