Rainbow trout are among the most studied farmed fish for welfare. Evidence-based standards for trout production provide a model for other aquaculture species.
Trout welfare science has advanced further than most other farmed fish species, providing evidence-based guidance on stocking density, water quality parameters, and slaughter humaneness. This reflects both the economic importance of trout farming and the relative tractability of conducting welfare research in a captive species. The evidence clearly shows that stocking density is the primary welfare determinant: high densities cause fin damage from contact, increased aggression, and chronic physiological stress responses that impair immune function and growth. Effective percussive stunning before slaughter, widely practiced in developed-country trout farming, eliminates conscious suffering during killing. The welfare standards developed for trout production provide a model framework that advocates are working to extend to other farmed fish species.