The susceptibility of sea trout juveniles to infection with salmonid alphavirus (SAV) and piscine orthoreovirus (PRV)

The aim of the current study is to compare the susceptibility of sea trout and salmon smolt juveniles (fry and parr) to infection with SAV and PRV. Atlantic salmon is susceptible to infection with both viruses. Salmon fry are susceptible and may develop disease, but no information exists for PRV. It is not known if sea trout will experience similar, less or worse infections and disease with neither SAV nor PRV. The study will generate data about the susceptibility of sea trout juveniles to viruses prevalent in salmon farming; namely SAV and PRV, and contribute to the knowledge on susceptibility of these species in different lifestages. Such data is necessary to evaluate the impact of diseases in fish farming on wild salmonid populations, especially so for juveniles (fry and parr) were such data is very limited. It may also support our screening results that suggest that sea trout is less susceptible to SAV and PRV than salmon. Four experiments will be conducted: To with fry (ca 0.2g) for SAV and PRV, and two for parr (ca 10g) for SAV and PRV, using both salmon (Salmo salar) and trout (Salmo trutta). In all four experiments we will use 6920 fish in total. These are divided into 1000 salmon parr shedders, 2226 trout fry, 754 trout parr, 2226 salmon fry and 754 salmon parr. The number of fish was selected after a thorough consideration for the minimum number needed at each sampling point and the number of sampling points required to study infection time-course. The limited size of fry (0.1-0.2 g), necessitates higher n compared to experiments with larger fish (e.g. parr and post- smolts). One entire fish will be needed for molecular analyses, and one fish for histological examinations. In addition, as examinations are conducted on different fishes, the n must be further increased in order to ensure statistical validity of comparisons.