Rainbow trout are among the most studied fish in welfare science, providing a benchmark for understanding stress, pain, and positive welfare indicators in aquaculture.
Rainbow trout welfare research has fundamentally changed understanding of fish sentience and welfare. Studies showing trout seek analgesics after noxious experiences, demonstrate preference for less aversive environments, and show consistent pain behaviour responses have built a substantial case for their capacity for negative welfare states. In aquaculture, key welfare challenges include high stocking density causing chronic social stress and aggression, pre-slaughter crowding and transport, and slaughter methods. Electrical stunning before slaughter — now standard in some European trout operations — provides immediate insensibility, representing a major welfare advance. Welfare indicators including opercular beat rate, colour change, and swimming pattern disruption allow on-farm welfare monitoring.