Response to selection for resistance against infectious pancreatic necrosis in Atlantic salmon (Salmo salar L.)

Abstract Resistance to infectious pancreatic necrosis virus (IPNV) has been included in a commercial selection program for Atlantic salmon since 2001. The IPN selection is based on bath challenge tests of several hundred families of first feeding fry, and the breeding value for each family is estimated from the resultant cumulative mortality rate. Since IPN selection is based on breeding values estimated from the results of a challenge test, it is difficult to evaluate the selection response in the population from generation to generation. Although a heritability of 0.31 has been estimated (unpublished results), we wanted to confirm the effect of selection for IPN resistance. The trial was carried out in two experiments where two groups of first feeding Atlantic salmon fry and postsmolts were challenged with IPNV: A) Families selected for high resistance to IPN, denoted as HR. B) Families from the same breeding population as A) selected for low resistance to IPN, denoted as LR. Both groups were challenged in two different tests: i) in fresh water in seven replicate tanks (7 × 100 fry). ii) in sea water after smoltification in five replicate tanks. Cumulative mortalities in the groups were significantly different. Group B) had more than double the mortality than group A), both in fresh water and sea water. The average cumulative mortalities in the A)/B) groups were 29.3%/66.6% and 32.0%/79.0% in fresh water and sea water, respectively.