Sea lice treatments in salmon farming cause significant acute welfare impacts. The methods used, their frequency, and the development of resistance all affect fish welfare outcomes in commercial aquaculture.
Each lice treatment event represents an acute welfare insult for the salmon population being treated. Mechanical treatments including thermal and freshwater methods cause significant physiological stress and mortality in a proportion of fish. The development of resistance means that treatment frequency has increased in some operations as efficacy declines, compounding cumulative welfare burden. Biological controls using cleaner fish offer welfare advantages over mechanical and chemical methods but raise their own welfare concerns about the cleaner fish themselves. Reducing lice burden through improved site selection and fallowing reduces the need for treatment and is the most welfare-positive long-term approach.