Rainbow and brown trout are farmed in significant numbers in the UK for both food and fishing restocking, with welfare standards varying enormously between operations.
Trout at high stocking densities experience chronic stress, elevated aggression and fin damage. They must compete intensely for food, creating subordinate individuals that are nutritionally deprived. Slaughter by asphyxiation in ice water causes prolonged loss of consciousness. Electrical stunning followed by percussive killing is significantly more humane but not universally adopted.