Diseases are introduced and spread by open-pen salmon farming
Overview
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“Studies on eDNA, the DNA floating freely in the marine environment which is not associated with fish, have demonstrated that salmon farms can act as a reservoir for viable pathogens, shedding large quantities into the marine environment around farms (Shea et al., 2020). […] Studies using eDNA have suggested that salmon farms pose a serious risk to wild Atlantic salmon and other vulnerable wild fish because of their capacity to introduce high levels of pathogens into the environment (Shea et al., 2020; Bastos Gomes et al., 2017).”
“Aquaculture environments have also been demonstrated to change pathogens from low virulence endemic strains to highly virulent strains with much higher rates of mortality. Kibegne et al., (2019) review into the emergence of novel viral diseases across the aquaculture sector found that “viral tourism” – the transfer of viruses through trade of biological material between salmon farms – has been responsible for the spread of several important diseases including VHSV, ISAV, SAV, and PRV, introducing these diseases to novel environments and hosts and facilitating the evolution of new strains.” Reference
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“Diseases caused by viruses are considered a major problem in fish farming in Norway. The most common viruses that occur in Norwegian fish farming are salmonid alphavirus (SAV), infectious pancreatic necrosis virus (IPNV), infectious salmon anemia virus (ILAV), piscine orthoreovirus (PRV) and piscine myocarditis virus (PMCV). These viruses annually cause 400 to 500 outbreaks of disease along the entire coast.”
Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research
Examples of some salmon farm pathogens and how they spread
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● “ISA is a severe and contagious viral disease in fish that first appeared in Norway in the 1980s and has since been detected in Canada, Scotland, Chile, the USA and the Faroe Islands.”
Norwegian Veterinary Institute
● “Infectious salmon anaemia (ISA) is a viral disease mainly affecting farmed Atlantic salmon in seawater, although some cases have been reported in freshwater. Other susceptible species include rainbow trout and brown trout.” Reference
● “Catastrophic disease outbreaks such as ISA in Chile have been linked to the importation of infected salmon eggs.” Reference
● “ISA virus (HPR0) circulates even after cleaning in hatcheries”
“It is one of several findings in a project led by the Norwegian Veterinary Institute.” Reference
● “The complexity and randomness of the occurrence of ISA in farming makes it difficult to say whether the areas with the most outbreaks will also have more frequent outbreaks in the future and thus increase the probability of infection to wild fish.”
Risk report Norwegian fish farming 2024 published by the Norwegian Institute of Marine Research
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“Infectious pancreatic necrosis (IPN) is a viral disease that is primarily associated with salmon fish farming. The IPN virus that causes the disease is globally spread, and has also been detected in a number of other fish. The sickness is the cause of substantial financial losses for the industry.” “Much suggests that the IPN virus can be transmitted both horizontally and vertically (via roe). Many individuals that survive an IPN episode will persistently be infected for a long period after the outbreak. These individuals will distribute the virus for long periods, which can lead to new outbreaks.”
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“Pancreas Disease is a serious disease that can lead to great economic losses for breeders due to poor growth and reduced slaughter quality. The disease spreads within a farm, to other farms within the same fjord system and through the transport of infected fish.”
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“Heart and skeletal muscle inflammation (HSMI) is a frequently fatal disease of farmed Atlantic salmon. First recognized in one farm in Norway in 1999, HSMI was subsequently implicated in outbreaks in other farms in Norway and the United Kingdom.” Reference
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PRV (Piscine orthoreovirus) has been shown to spread from Norway and has been detected in pacific farmed and wild fish species as far north as Alaska, and as far south as Chile. Reference
For a more exhaustive list of pathogens plaguing open-pen salmon farming, visit Appendix A (pg 19) of the recent report The Reality Gap: an examination of Scottish farmed salmon published by the charity WildFish