Disease is a major welfare challenge in farmed rainbow trout, with proliferative kidney disease, bacterial infections, and ectoparasites requiring management approaches that balance welfare and production.
Disease welfare in farmed trout is intimately connected to environmental management because many pathogens are temperature-dependent and thrive in the warmer water temperatures that accompany climate change. Proliferative kidney disease (PKD) causes kidney swelling, anemia, and immune compromise in affected fish - a chronic condition that impairs welfare throughout the infection period and can be fatal at high severity. Bacterial furunculosis causes acute tissue destruction and systemic infection that, without treatment, results in painful systemic septicemia. The welfare benefit of early disease detection and treatment is clear, but the challenge is that fish in large net pens cannot be individually monitored - disease identification relies on population-level behavioral changes that may indicate significant welfare compromise has already occurred.