Rainbow trout are among the most widely farmed fish in temperate regions, with specific welfare challenges in flow-through systems including stocking density, disease management, and slaughter.
Trout welfare in flow-through systems is shaped by the tension between the natural behaviour of a territorial species and the densities required for commercial production. Wild rainbow trout are solitary and territorial; farmed trout at commercial densities experience continuous social stress and aggression. Fin condition is a reliable welfare indicator that deteriorates with increasing density and aggression. Water quality in flow-through systems depends critically on the quality of the incoming water source and the stocking management of each raceway. Slaughter welfare for trout has improved in some markets but remains inconsistent, with percussive stunning sometimes replaced by CO2 asphyxiation or ice immersion.