Evidence-based information about farmed rainbow trout: fin damage as a welfare indicator for animal welfare improvement.
Damaged fins indicate that fish have experienced aggression or abrasion against tank surfaces. Dorsal and caudal fin erosion is associated with high stocking densities and poor water quality. Fish with severe fin damage are more susceptible to infections and have compromised welfare compared to fish with intact fins. Fin condition scoring is an accessible, non-invasive welfare assessment tool.