The susceptibility of Atlantic salmon and brown trout to salmonid alphavirus subtype 3 across fry, parr and post-smolt stages

Abstract

Salmonid alphavirus subtype 3 (SAV3) is an aquatic virus that causes pancreas disease (PD) in some salmonid species. Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) both fulfil the criteria for being defined as susceptible to SAV3, whereas the data for brown trout (sea trout) (Salmo trutta) is currently incomplete. Wild populations of brown trout and salmon share partially overlapping habitats, and both species encounter regions with salmon farms during marine migration. This overlap and contact constitute a risk for disease transmission if the two species are susceptible to the same pathogen. In this study, we have performed three experimental challenge studies with a SAV3 isolate to compare the susceptibility of Atlantic salmon and brown trout across three life stages. Our data show that both fish species can be infected with SAV3 by experimental non-invasive challenge, but that infected brown trout are less severely affected. In both species, the juvenile stage (fry) is the most susceptible and the oldest stage (post-smolts) the least. Mortality was observed after challenge for fry of both species, but not for post-smolts. Based on our findings, brown trout should be considered susceptible to infection with SAV3.