Gill health is one of the most critical welfare parameters in Atlantic salmon farming. Amoebic gill disease, sea lice, jellyfish stings and other insults impair respiratory function and cause significant welfare harm.
Gill health welfare is respiratory health welfare: a salmon with damaged gills is permanently breathless, experiencing chronic respiratory discomfort that limits activity, feeding and immune function. Gill damage from multiple simultaneous insults (AGD + sea lice + jellyfish) is compounding - the cumulative welfare cost exceeds each individual source. Treatment decisions involve acute stress from freshwater bathing weighed against chronic stress relief from parasite reduction. Prevention through snorkel systems, fallowing and selective breeding for AGD resistance is welfare-preferable to repeated reactive treatment. The welfare of salmon is fundamentally respiratory - protecting gill health protects welfare at the most basic physiological level.