Piscine Reovirus (PRV)
Piscine Reovirus (PRV) is a highly contagious virus affecting salmon in BC A 2013 study concluded that PRV in BC was likely imported from Norwegian fish farms where the farmed fish originated. Because of the high density of salmon in fish farms, highly toxic variants of PRV have been able to live and prosper. 
In Norway, PRV has been linked to Heart and Skeletal Muscle Inflammation (HSMI), which causes problems with the heart, liver, spleen, and other internal organs in salmon. HSMI has a mortality rate of 20%.  It is a deadly disease that can quickly devastate a salmon population.
PRV is extremely contagious. 95% of farmed salmon in BC test positive for PRV.  The dense nature of open net pen fish farms allows PRV to mutate to higher levels of virulence. Most concerning, PRV can be spread through water, making wild Pacific salmon who come in close proximity to open net pen fish farms highly susceptible to the virus. PRV is a powerful example of what happens when viruses are left to replicate in open net pen fish farms.