Amoebic Gill Disease in Salmon: Welfare Challenges and Treatment Approaches

Amoebic Gill Disease (AGD) caused by Neoparamoeba perurans is the most significant health and welfare challenge in Atlantic salmon farming, causing respiratory distress that requires intensive management.

Key Facts

AGD causes gill epithelial proliferation that impairs oxygen and ion exchange, causing respiratory distress
Prevalence increases with sea temperature - AGD risk rises substantially above 14 degrees C
Freshwater bathing is the primary treatment, achieving temporary parasite clearance but requiring repeated application
Treatment frequency in some farms reaches every 2-3 weeks at peak risk, with each treatment causing handling stress
Hydrogen peroxide treatment is an alternative to freshwater bathing with different welfare and environmental profiles
Genetic selection for AGD resistance is under active investigation as a long-term welfare solution
Gill scoring using 0-6 scale post-mortem provides the key welfare monitoring metric for AGD burden

Welfare Considerations

AGD welfare management creates a treatment paradox: the disease causes respiratory distress, and the primary treatment (freshwater bathing) involves handling and environmental change that cause acute stress. This means that managing AGD involves choosing between untreated disease-related suffering and treatment-related stress, neither of which is cost-free for the fish. The welfare optimization seeks to treat at the point where disease burden justifies treatment stress, and to minimize treatment stress through careful handling protocols. Long-term solutions - genetic selection for resistance, vaccines, and improved site selection - would resolve this paradox by preventing AGD rather than managing it. Climate change makes AGD management increasingly critical as warming seas extend and intensify peak risk periods.

What You Can Do

Choose salmon from farms that publish AGD monitoring data and have low gill score averages indicating good disease management
Advocate for research funding for AGD vaccine and genetic resistance programs as long-term welfare solutions
Support site selection regulations that favor locations with lower temperatures and better water exchange
Ask salmon producers about their AGD treatment frequency and welfare protocols for freshwater bathing procedures
Support climate policy that reduces ocean warming, as temperature is the primary AGD risk driver