Exercise training effects on disease resistance are dependent on training regimes and inherent swimming performance in Atlantic salmon

Atlantic salmon juveniles were screened for swimming performance and separated into either poor or good swimmers. After ten weeks of rearing in fresh water, during which both swimming performance groups were part of an exercise training experiment, fish were transferred to seawater and challenged with infectious pancreatic necrosis virus (IPNV) in a co-habitation test. When mortality curve levelled out (45 days post commencement of challenge test), fish that had previously been categorized as good swimmers displayed a significantly higher survival (86.1%) compared to poor swimmers (77.6%). Global gene expression analyses were performed to search for disease resistance correlates. Cardiac ventricle expression of 21 genes was greater in poor swimmers than in good swimmers. These genes were previously classified as virus-responsive genes (VRGs), being reliable markers of viral load. This suggested that inherent swimming performance is associated with higher disease resistance. Atlantic salmon post-smolts belonging to groups previously classified as either poor or good swimmers were challenged with infectious pancreatic necrosis virus (IPNV). Heart ventricle was sampled from challenged and unchallenged fish on day 45 post-commencement of the challenge (when no more mortalities were registered). Nine poor swimmers and nine good swimmers were hybridized against a common reference sample composed of nine unchallenged fish.