Clonal salmon – Vaccination and infection response variability

The economic importance of salmon (Salmo salar) has led to intensive research on this species with concomitant large numbers of fish used in research. One of the caveats in salmon research is the large individual variation in responses which have spurred to the creation of clonal salmon lines at the Institute of Marine Research. The reasons for this is that decreased (or absence of) genetic variation is expected to lead to decreased individual response variation in the fish, which may facilitate the completion of experiments with fewer fish without losing strength in the conclusions. However, the expected reduced variability needs confirmation, and the present experiment will investigate phenotypic and transcriptomic variability in two clonal and two non-clonal lines of salmon. Specifically, we will investigate the responses to vaccination against SAV and Aeromonis salmonicida and the variability in susceptibility to the same pathogens. 200 fish from each line will be utilized in the experiment (800 fish in total). As the aim of the experiment is to validate clonal salmon as a more accurate replacement of non-clonal salmon as experimental fish, a replacement with other species in the present experiment is not possible. The number of fish in the experiement is chosen based on experience with vaccination, infection and transcriptomic analyses of salmon. The experiments will be conducted at the quarantine-facility at IMR, Bergen. The experiment will comprise vaccination, boosting, smoltification and pathogen challenge in that order. The duration of the experiment will be 17 weeks, while infection will be performed 2 weeks before experiment termination. The fish will experience pain during vaccination and boosting and a level of stress during handling even though great care will be taken to reduce stress to a minimum. Approximately half of the fish (90 fish from each line) will be infected with either SAV or Aeromonis salmonicida which is an obvious source of discomfort and pain. The infected fish will be monitored closely and sampling will be implemented according to the condition of the fish which is necessary to secure data from living fish and to reduce the suffering of the infected individuals. On sampling the fish will be killed by an overdose metomidate and benzocaine which will reduce the experience of pain while some stress experienced during sampling is unavoidable.