Rainbow trout are one of the most widely farmed fish species, with welfare challenges related to stocking density, water quality, and slaughter methods.
Farmed rainbow trout welfare has received more scientific attention than most other farmed fish species, partly because of their commercial importance in Europe and partly because of their physiological similarities to salmonids. Key welfare problems include high stocking densities that impair swimming behaviour and increase aggression, water quality problems that cause chronic gill irritation, and slaughter methods that cause suffering. Carbon dioxide stunning — once widely used — is now understood to cause pain and distress before loss of consciousness, and its replacement with percussive or electrical stunning is a significant welfare improvement.