Chemical treatments used to control sea lice on farmed salmon cause stress and mortality in treated fish while also harming non-target marine invertebrates in surrounding waters.
The welfare of salmon subjected to chemical sea lice treatments is compromised in multiple ways. Bath treatment confines fish at high density under additional chemical stress. Hydrogen peroxide at incorrect temperatures or concentrations causes ocular damage that has been photographically documented in treated fish. The stress response from treatment is measurable and prolonged. The cycle of treatment, resistance development, and escalating chemical use represents a welfare treadmill. Closed containment systems that prevent sea lice infestation entirely eliminate this welfare burden alongside the wild fish impacts.