Fish welfare and color of skin and fillets of Atlantic Salmon from two genetic lines exposed to repeated hypoxia prior to harvesting

Oxygen is a fundamental necessity for the fitness and survival of Atlantic salmon. Hypoxia is reduced access to oxygen and low levels of oxygen in body tissues, which affects the welfare, immune response, and product quality of Atlantic salmon. The severity of hypoxia is dependent on exposure time, the size of the fish, life stage and genetics. In the present study, two genetic lines that were selected for fillet color alone (RED and PALE), were exposed to repeated hypoxia (one, two or three times) and the effects on biometric parameters, welfare, skin color, fillet color and fillet quality were evaluated. The body weight, condition factor, and fillet yield of the PALE genetic line was higher compared to the RED genetic line, and hypoxia had no effect on these biometric parameters. The cardiac somatic index of the RED genetic line was higher compared to the PALE genetic line, and hypoxia had no effect. The operational welfare indicators were all affected by exposure to repeated hypoxia. Most of the indicators were not affected by genetics, however the snout damage score was higher for the RED genetic line compared to the PALE genetic line. The fillet color was redder and the astaxanthin content was higher for the RED genetic line compared to the PALE genetic line, but hypoxia did not negatively affect the fillet color. The skin of NQC got darker and less blue with exposure to repeated hypoxia. The skin color of anterior fillets was not affected by hypoxia. The fillet texture got softer as the fish were exposed to repeated hypoxia. Genetics affect color and biometric traits, and hypoxia negatively affects welfare and darkens the skin color of NQC. There needs to be more research that covers the interaction between heart health and astaxanthin retention. In conclusion, further research is needed to look at the performance and mechanisms behind the differences between the two genetic lines. The astaxanthin retention and disposition could be genetically linked to biometric traits and heart health and could be a potential topic suitable for further research