Rainbow trout are one of the most widely farmed fish in Europe and North America. Their welfare across production stages is increasingly scrutinized as evidence of fish sentience accumulates.
Rainbow trout welfare has been studied more comprehensively than most farmed fish species, reflecting both their economic importance and research investment in the UK, Norway, and elsewhere. Key welfare hazards include: crowding stress during grading and harvest, handling injuries, parasitic infections (particularly sea lice in sea cage systems), bacterial and viral disease, poor water quality, and inadequate stunning at slaughter. Positive welfare indicators include active swimming behavior, normal feeding responses, good body condition, low injury rates, and behavioral diversity. The EFSA opinion on trout welfare (2008) identified both hazard categories and potential welfare indicators for on-farm assessment. Slaughter welfare varies considerably: percussive stunning followed by exsanguination is the most humane option and is used by leading producers. Live chilling in ice slurry — still common — causes prolonged consciousness during cooling and subsequent death by asphyxiation.