Rainbow trout are one of the most widely farmed fish species globally. Their welfare is affected by stocking density, water quality, handling, and slaughter methods — all of which can be improved with existing knowledge.
Trout welfare in intensive systems is primarily determined by stocking density and water quality. At densities that maximise production efficiency, individual fish cannot avoid contact with conspecifics, fin damage from aggression is widespread, and competition for oxygen and space causes chronic stress. Water quality failure — particularly oxygen depletion and ammonia accumulation — causes gill damage and respiratory distress that fish cannot escape. Slaughter of trout without prior stunning means fish die by asphyxiation or live bleeding while still conscious. The welfare improvements available to trout farmers are well-evidenced: density reduction, robust water quality monitoring, and percussive or electrical stunning before slaughter would substantially reduce suffering with manageable cost implications.