Active immunisation of Atlantic salmon, at least 2g, to reduce mortality from furunculosis caused by Aeromonas salmonicida. The time for development of protective immunity will depend on the water temperature. 336 degree-days should be allowed between vaccination and anticipated exposure to infection (e.g. 28 days at a water temperature of 12°C).

Under laboratory conditions, after immersion vaccination of very small (2g) fish, a duration of immunity of up to 1080 degree days (90 days at 12°C) has been demonstrated, although the level of protection waned during this period (relative percentage survival 77% at 28 days, 42% at 90 days). No laboratory studies have been carried out to investigate duration of immunity after injection vaccination. Under field conditions, after injection vaccination of larger fish (35g) there is some evidence of duration of immunity of up to 4 months, and up to 6-9 months where immunity to vaccination is likely to have been boosted by natural challenge.