Rainbow trout are among the most studied farmed fish species for welfare purposes, yet commercial practice still falls significantly short of research-informed standards.
Rainbow trout welfare science is relatively advanced compared to most farmed fish species, providing clear evidence that current commercial practices cause significant suffering. Chronic social stress from dominance hierarchies in crowded systems leads to measurable suppression of immune function and growth. Slaughter without effective stunning — including CO2 narcosis, which is slow and aversive — is common in smaller operations. The existence of welfare-improving alternatives (lower densities, effective stunning methods, feeding system design to reduce aggression) makes ongoing welfare failures less excusable. Rainbow trout are a proving ground for fish welfare improvement: what works here can be adapted for other species.