Stress resistant salmon and trout

Selection for reduced stress responsiveness in salmon and trout leads to reduced size variation, enhanced growth, reduced feed waste, improved disease resistance, and improved animal welfare. Current indicators of stress and stress responsiveness in fish are however difficult to apply outside the laboratory. We suggest using dermal pigmentation as a visual indicator of stress and disease resistance, according to the following rationale: Salmon and trout skin vary from immaculate to densely spotted, with black spots formed by eumelanin-containing chromatophores. Spotted individuals show a reduced cortisol response to stress, and markedly reduced rates of infection from ectoparasitic sea lice. Current status is that lines of rainbow trout have been selected for high (HR) and low (LR) stress responsiveness over 6 generations. Similar lines can be created in Atlantic salmon using melanisation markers. The potential for increased competitiveness and improved animal welfare by selection for stress responsiveness is most pronounced when fish are subject to suboptimal and stressful rearing conditions, for instance in water recirculation systems, areas with high pathogenic load, or areas with compromised water quality. Pilot cases for testing the product, eggs and offspring of stress resistant fish, are therefore sought among producers of salmon or trout in novel, "problematic" areas for the production of salmonid fish, such as continental Europe (areas with limited water resources, trout) or Chile (salmon). Strategic partnerships and financing to maintain and develop selected lines of rainbow trout and Atlantic salmon is also needed.