Rainbow trout farming faces disease challenges including bacterial kidney disease, furunculosis and viral haemorrhagic septicaemia. Disease management decisions profoundly affect both welfare and sustainability.
Disease in farmed trout causes chronic suffering: affected fish show reduced appetite, abnormal swimming, lesions and eventually fatal systemic infection. The welfare challenge is that disease management in aquaculture often prioritises survival rate and antibiotic use reduction over individual fish welfare. Fish with chronic, incurable conditions like BKD may survive but suffer throughout their lives. Vaccination has been a genuine welfare advance by reducing the need for antibiotic treatment and the disease burden that treatment would otherwise address imperfectly. The next frontier is identifying and reducing chronic, subclinical disease states that reduce welfare without causing obvious mortality.