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Selection for improved disease resistance -testing unvaccinated or vaccinated fish?

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Kjetil Aune

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kjetil.aune@nofima.no

10th International Symposium on Genetics in Aquaculture (ISGA x); Bangkok, Thailand, 2009-06-22–2009-06-26

Drangsholt, Tale Marie K; Gjerde, Bjarne; Bentsen, Hans Bernhard; Bentsen, Hans; Ødegård, Jørgen

Farmed Atlantic salmon (Salmo salar) are selected for increased resistance to furunculosis (caused by Aeromonas salmonicida) based on challenge test survival of unvaccinated fish. However, nearly all grow-out salmon are vaccinated. The objective of this study was to determine whether selection for improved resistance to furunculosis based on challenge test survival of unvaccinated fish will be effective with respect to furunculosis resistance in vaccinated fish. The data was obtained from challenge tests of 150 families from the Norwegian breeding company SalmoBreed. From each family a random sample of unvaccinated fish and fish vaccinated with full and reduced dose was challenged with A. salmonicida by co-habitation. The challenge test of unvaccinated fish was performed with co-habitation in a separate tank. The heritability for survival to furunculosis was 0.51 ±0.05 in unvaccinated fish (0.29 ±0.03 on the observable scale), and heritability in fish vaccinated with full and reduced dose was 0.39 ±0.06 and 0.34 ±0.06, respectively (0.24 ±0.04 and 0.22 ±0.04 on the observable scale). The genetic correlation between survival of unvaccinated and vaccinated fish (full and reduced dose) was moderately positive (0.32 ± 0.13 and 0.55 ± 0.11). The genetic correlation between survival of fish vaccinated with full and reduced dose was high (0.90 ±0.06). The relatively high heritability of survival in unvaccinated fish implies that selection based on survival in unvaccinated fish will be efficient if the long term breeding goal is to supply the industry with fish that survive the disease without vaccination. This selection strategy will also produce a desired, but smaller indirect response in survival to furunculosis in vaccinated fish due to the positive genetic correlation between the traits. However, selection for improved survival in vaccinated fish will be considerably more efficient if widespread use of this type of vaccine is inevitable also in the long run.

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