Fig 4. Salmon production cycle.

The production cycle of Atlantic salmon depicting the timing of IPN vaccination, challenge and convalescence. A indicates the immune induction period being the period between vaccination and challenge. Note that vaccination is carried out at the parr stage in freshwater before smoltification. B indicates the time of challenge at the post-smolt stage soon after transfer to seawater, which conforms to the time when most outbreaks occur during the Atlantic salmon production cycle. C shows the period after lethal challenge when the survivors become carriers or persistently infected with post challenge virus during convalescence.