While there are several diseases that impact Atlantic salmon aquaculture, Infectious Salmon Anemia Virus (ISA or ISAv) is the most influential disease. ISA first appeared in Norwegian salmon farms in 1984, and have since impacted farms in the Faroe Islands, Scotland, Chile, the US, and Canada (Asche 406). ISA is a highly contagious disease, previously known as Hemorrhagic Kidney Syndrome, in which affected fish experience anemia, or a lack of red blood cells.
The disease initially has a low mortality rate and can be difficult to detect; however, if the disease is not treated, mortality rates can increase to anywhere between 90 to 100%, potentially wiping out entire farms (CFSPH 1). Currently, there is an incomplete epidemiology, where even the means of transmission is uncertain. The disease is spread through horizontal transmission (from one member of species to another in which there is not a parent-offspring relationship), likely through gill to gill interactions, but possibly through either ingestion or parasites (CFSPH 2). The disease can also be spread asymptomatically (without showing symptoms) from one Atlantic salmon to another or even through other salmonids such as different species of salmon and trout (CFSPH 2). Because the disease is spread through horizontal transmission, regardless of the actual means of transmission, the transmission rate would increase when organisms are in close proximity to one another, such as within a tank or net pen as seen in aquaculture. Despite the incomplete epidemiology, ISA can be treated using chemical disinfectants or prolonged exposure to extreme pH levels, temperatures, or ultraviolet radiation (CFSPH 5). Furthermore, Aldrin et al. show that areas with high concentrations of fish farms that are affected are likely due to transmission of the disease from neighbors (see Figure 2). This demonstrates that ISA is not only difficult to combat in a single farm, but the outbreak affects farms around it as well.
J. Cody Herron is a junior Physics major and Genomics minor at Davidson College.