Preventing heart pathology in farmed Atlantic salmon

Cardiac pathology in farmed salmon is increasing problem for the fish-farming industry, and diagnostic work and biological understanding is lacking behind in meeting this challenge. Pre-slaughter mortality affects large production fish often in connection with handling and transport. The implications for production economy, management, and animal welfare may be severe, as affected fish are otherwise typically in good condition and show no external signs of disease. Autopsy will however often reveal conges tion with ascites and flaccidity of the cardiac ventricle. Biologically, the salmonid heart is a very plastic organ, adapted to meet dramatic life-history changes during for instance migration and spawning. Plastic changes is, however, also often associat ed with an increased risk of myocardial remodeling and dysfunction. In other animal groups, including humans, stress is clearly associated with a poor prognosis in individuals with established cardiac pathology and disease. The mechanism linking stress re sponses to the development of cardiac disease is poorly understood in fish, but mortality tends to occur in association with stressful interventions. It was also recently reported that heritable variation in stress responsiveness is important, with stress -sensitive individuals tending to develop ventricular hypertrophy. In the current project, we will evaluate two strategies towards understanding and combating heart pathology in farmed Atlantic salmon: Selective breeding for increased stress resistance, a nd implementing procedures which render the fish more robust under conditions of stress. The project is carried out within a network of highly acknowledged national and international partners, and a committed strategy for publication and communication wit h end users will be employed. This will both increase fundamental understanding of the problem, and furnish the industry with a set of possible countermeasures.