Krill supplement does not reduce virus load or heart pathology during PRV-3 infection in rainbow trout under experimental conditions

Piscine orthoreoviruses pose a significant challenge to salmonid aquaculture, as there are currently no preventive measures, like vaccines, available. Piscine orthoreovirus genotype 3 (PRV-3), now renamed Orthoreovirus piscis , has been linked to disease in rainbow trout ( Oncorhynchus mykiss ) farmed in recirculating aquaculture systems (RAS), and has a high prevalence in Danish RAS. Previous studies have demonstrated that functional feeds can reduce the heart inflammation caused by PRV-1 in Atlantic salmon ( Salmo salar ). This study aims to determine whether functional feeds have a similar effect on rainbow trout infected with PRV-3. Specifically, we investigated the impact of a krill meal enriched diet on heart inflammation, anemia, and viral RNA load in rainbow trout exposed to PRV-3. The fish were pre-fed with either a control diet or enriched diet for six weeks prior to challenge with PRV-3. The results showed no significant differences in viral RNA load, hematocrit levels or heart pathology between the diets. However, PRV-3 exposed fish fed with the enriched diet exhibited significantly higher weight gain compared to those on the control diet. These findings suggest that while krill meal enhances growth performance, it does not reduce PRV-3-induced heart pathology in rainbow trout. Further research is needed to explore the underlying mechanisms and potential benefits of dietary interventions in managing PRV-3 infections.