Rainbow trout are among the most widely farmed fish in Europe. Their welfare in intensive raceways and net pens, and during slaughter, has received significant research attention that is informing policy reform.
Rainbow trout welfare is better evidenced than almost any other farmed fish species. Research demonstrates stress responses to crowding, nociceptive responses to harmful stimuli, and impaired welfare from poor water quality. CO2 stunning — widely used in industry — causes aversion before unconsciousness: trout actively avoid CO2-enriched water, indicating it is not immediately comfortable. Electrical stunning when properly applied achieves immediate unconsciousness. Welfare policy for rainbow trout is one of the most technically advanced areas of farmed fish welfare.