Vaccinated fish welfare: protection versus side-effects

Active immunisation of fish involves a number of potentially harmful procedures like handling, anaesthesia or injection of more or less toxic substances. Adjuvanted vaccines may cause inflammation, granuloma and pigmentation at the site of injection. Intraperitoneal administration of oil-adjuvanted vaccines to Atlantic salmon pre-smolts has occasionally resulted in impaired growth and reduced carcass quality. The consequences of such vaccination for fish welfare may therefore be questioned. With respect to furunculosis caused by Aeromonas salmonicida, scientific data suggest, however, that only oil-adjuvanted vaccines are protective throughout the production cycle of farmed salmon. Data are presented to show that salmonids are highly at risk to epizootics if left unprotected against this or other endemic diseases. A panel of parameters partly adopted from experimental animal medicine is proposed to assess the impact of vaccine side-effects in farmed fish. In intensive salmon aquaculture systems, reduced disease risks are thought to justify the observed level of side-effects following current vaccination practices. For future fish vaccines, reduction of side-effects without compromising long-term protective immunity constitutes a challenging goal.