Rainbow trout is one of the most studied farmed fish species for welfare, yet production conditions still routinely cause chronic stress, injury, and poor welfare outcomes.
Rainbow trout welfare research provides one of the clearest pictures of how production conditions cause chronic suffering in farmed fish. At high stocking densities, subordinate trout are excluded from feed, suffer more injuries, and show persistently elevated cortisol. Fin erosion — partial or complete loss of fins from abrasion and biting — is painful and impairs normal swimming. Cataracts develop in poorly managed farms from nutritional deficiencies and UV exposure, causing visual impairment. Grading procedures — sorting fish by size using crowding boards and nets — cause acute stress and physical injury. The welfare science exists to guide improvements; the barrier is implementation at scale across an industry where welfare costs money.