Vaccination has transformed salmon aquaculture by dramatically reducing antibiotic use. Understanding the welfare implications of vaccination procedures and their net benefit is important for assessing salmon welfare in the industry.
Salmon vaccination illustrates the complexity of welfare trade-offs in aquaculture. Individual vaccination causes acute stress from anaesthesia and the injection procedure, and oil-adjuvant vaccines can cause chronic injection site reactions and internal adhesions that may impair normal organ function and swimming behaviour. However, the alternative - unvaccinated fish susceptible to bacterial outbreaks causing mass mortality from diseases that can cause severe suffering before death - represents a far worse welfare outcome. The dramatic reduction in antibiotic use also reduces the welfare costs associated with antibiotic-resistant infections. Continuing refinement of vaccination procedures, anaesthesia protocols, and vaccine formulations to minimise side effects is the appropriate welfare response.