Gill health is a leading cause of mortality and welfare compromise in farmed Atlantic salmon, while sea lice infestation causes skin and tissue damage. Managing both requires integrated approaches that minimise suffering.
Gill disease and sea lice represent two of the most significant welfare challenges in Atlantic salmon farming, and they are often interconnected - sea lice damage predisposes to secondary bacterial and fungal gill infections. Amoebic gill disease causes progressive gill lamellar fusion, haemorrhage, and hyperplasia, severely compromising respiratory function and causing hypoxia-related distress. Sea lice feeding causes tissue erosion that is directly painful and damages osmoregulatory function. Treatment procedures themselves carry welfare costs: hydrogen peroxide bathing causes avoidance behaviour and temporary respiratory compromise; mechanical treatments can cause scale and fin damage. The increasing use of wrasse and lumpfish as cleaner fish to control sea lice has created a new welfare dimension, as these species have distinct needs often poorly met in salmon farming contexts.