Rainbow trout are one of the most widely farmed freshwater fish globally, with welfare challenges around stocking density, water oxygen levels, and the handling and slaughter practices used at harvest.
Rainbow trout farmed at high densities experience chronic social stress from crowding, competition for space, and increased aggression. Fin damage — from biting by conspecifics — is a welfare indicator of density and social stress that is measurable and directly linked to housing conditions. Oxygen depletion events cause mass mortality through asphyxiation. The harvest and slaughter process for trout varies enormously in welfare impact: electrical stunning followed by gill cutting offers near-instantaneous loss of consciousness, while CO2 narcosis causes distress before effective sedation and live chilling causes prolonged conscious distress. Research-based stocking density guidelines exist but regulatory minimum standards are often set at higher densities than welfare research would support.