Infectious salmon anaemia (ISA) is a serious viral disease of farmed Atlantic salmon, Salmo salar L., caused by
infectious salmon anaemia virus (Isavirus, Orthomyxoviridae). An ISA outbreak may vary when it comes to
clinical manifestations and mortality levels. Some outbreaks have an aggressive development with an escalating
mortality level (up to 90%). At these sites, efficient removal of dead fish can be a major challenge. Removal of dead
fish is an important fish health preventive measure implemented at marine sites. In the present study we have
examined the infection risk the dead fish may represent for the remaining fish at the site by examining both
tissues from fish that died from ISA, and from the surrounding water (0–120 h post mortem). The aim was to
examine for how long infectious virus particles could be retrieved from dead salmon as this could indicate if
such material may pose a risk for spreading of ISA virus. Although viral RNA was detectable in water from
decomposing salmon by real-time RT-PCR, no infectious particles could be obtained fromwater either by inoculating
cell cultures or by injecting water samples into fish. Nevertheless, the study showed that infectious virus
particles could be retrieved from heart tissue of dead fish for more than 4–5 days post mortem.
Thus, daily removal of dead fish is an important preventative measure during ISA outbreaks. It is also of importance
to removemoribund fish with ISA as these continue to produce and shed virus and may represent a greater
risk with respect to the transmission of virus than the fish that are already dead.