Heart and skeletal muscle inflammation (HSMI) is a significant viral disease in farmed Atlantic salmon with direct welfare implications for billions of fish. Understanding it illuminates the health-welfare connection.
HSMI represents the intersection of intensive aquaculture, emerging disease and animal welfare. Fish with compromised cardiac function from HSMI cannot swim effectively, maintain position in currents, access food at normal rates or escape threatening stimuli - each of these impairments reduces quality of life. The disease's connection to production intensity (high stocking density, high growth rate genetics) means that the same commercial pressures driving profitability also drive disease susceptibility. Until an effective vaccine is available, welfare improvements for HSMI must focus on reducing stocking density, selecting more robust genetics and monitoring cardiac welfare indicators in affected populations.