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Health monitoring in wild anadromous salmonids -Evidence of absence or absence of evidence?

Ase Helen Garseth1*, Eirik Biering1 and Arne Skorping2
  • 1 Norwegian Veterinary Institute, Section for Environmental and Biosecurity Measures, Norway
  • 2 University of Bergen, Department of biology, Norway

During the last four decades salmon farming has developed from a small scale supplementary enterprise to the second most important industry in Norway. The growth in the industry has coincided with a decline in wild salmonid populations (Anonymous 2001), and a connection between the two has been suggested. The negative impact of escapees and of the salmon louse Lepeophtheirus salmonis salmonis has to a large degree been acknowledged (Anonymous 2009). Now, a plausible question is whether the increasing number of viral diseases within salmon farming will contribute to the decline (Anonymous 2016). The scientific advisory committee for Atlantic salmon management in Norway has assessed the role of infections associated with farming activity to be of less importance than escaped farmed salmon and salmon lice. However, they also conclude that there is a lack of knowledge about this factor and that the uncertainty about future development is high (Anonymous 2009).Compared to the conditions in wild host populations, large scale intensive farming of animals represents a dramatic change in conditions for virus growth and transmission. The observed emergence of viral diseases within salmon farming should therefore be expected. It is also suspected that disease outbreaks in fish farms will lead to increased infection pressure on wild stocks (Raynard et al. 2007). Investigating how viral diseases within salmon farming can have an impact on wild stock is methodologically challenging. Nevertheless, establishing knowledge about the occurrence and distribution virus within wild populations is regarded as an important initial step in that investigation (Anonymous 2007). Recent research and health monitoring initiatives in wild salmonids in Norway have provided information and some insight. Piscine orthoreovirus (PRV), the causative agent of heart and skeletal muscle inflammation (HSMI), is a common finding in returning wild brood fish (Biering et al. 2013, Garseth et al. 2013). In contrast, infectious pancreatic necrosis virus (IPNV), infectious salmon anemia virus (ISAV), salmonid alphavirus (SAV) and piscine myocarditis virus (PMCV) are rarely detected (Garseth et al. 2012, Biering et al. 2013, Garseth et al. 2013, Garseth et al. 2015, Madhun et al. 2016) and there is a set of discrepancies with regards to how the results are interpreted. Cross sectional studies have their limitations and should be seen in conjunction with other sources of information. More specifically, concluding that the absence of virus positive wild salmonids proves that viral diseases within salmon farming have no impact om wild populations is potentially a dangerous journey. We argue that this conclusion is inadequate because it does not take into account the dynamics of disease in wild populations and the relationship between parasite prevalence, virulence and transmission. The aim of the presentation is thus to discuss alternative interpretations of recent results from health monitoring in wild anadromous salmonids in Norway.

References

Anonymous (2001). The status of wild Atlantic salmon: A river by river assessment, WWF: World wildlife fund. http://wwf.panda.org/wwf_news/?3729/The-Status-of-Wild-Atlantic-Salmon-A-River-by-River-Assessment

Anonymous (2009). The status of Norwegian salmon stocks in 2009 and catch advice. Scientific Advisory Committee for Atlantic Salmon Management in, Norway, Scientific Advisory Committee for Atlantic Salmon Management in Norway. 1: 1-230.

Anonymous (2007). Developement of a monitoring system to improve knowledge regaring the impact of escaped farmed fish on wild fish stocks. T. Magnussen, C. E. Arnesen, M. Binde et al. Trondheim/Oslo/Bergen, Directorate of Fisheries, Norway: 88.

Anonymous (2016). Fiskehelserapporten 2015. www.vetinst.no Veterinærinstituttet.

Biering, E., A. S. Madhun, C. H. Isachsen, L. M. Omdal, A. C. Bårdsgjære Einen, Å. H. Garseth, P. A. Bjørn, R. Nilsen and K. Egil (2013). Annual report on health monitoring of wild anadromous salmonids in Norway. www.vetinst.no Norwegian Veterinary Institute and Institute of Marine research.

Garseth, Å. H., E. Biering and T. Tengs (2012). "Piscine myocarditis virus (PMCV) in wild Atlantic salmon Salmo salar." Diseases of aquatic organisms 102(2): 157-161.

Garseth, A. H., E. Biering and T. Tengs (2013). Corrigendum: Piscine myocarditis virus (PMCV) in wild Atlantic salmon Salmo salar." Dis Aquat Organ 104(3):(3).

Garseth, A. H., C. Fritsvold, M. Opheim, E. Skjerve and E. Biering (2013). "Piscine reovirus (PRV) in wild Atlantic salmon, Salmo salar L., and sea-trout, Salmo trutta L., in Norway." Journal of Fish Diseases 36(5): 483-493.

Garseth, A. H., A. S. Madhun, E. Biering, C. H. Isachsen, I. Fiksdal, A. C. Bårdsgjære Einen, B. Barlaup. and E. Karlsbakk (2015). Annual report on health monitoring of wild anadromous salmonids in Norway. www.vetinst.no Norwegian Veterinary Institute, Norway.

Madhun, A.S., A.H Garseth, A.C. Einen, I.Fiksdal, H. Sindre, S Karlsson, E.Biering, B. Barlaup and E. Karlsbakk (2016). Annual report on health monitoring of wild anadromous salmonids in Norway. www.vetinst.no Norwegian Veterinary Institute, Norway.

Raynard, R. S., Wahli, T., Vatsos, I. and Mortensen, S. (2007). Review of disease interaction and pathogen exchange between farmed and wild finfish and shellfish in Europe. Review of disease interaction and pathogen exchange between farmed and wild finfish and shellfish in Europe. R. S. Raynard, T. Wahli, I. Vatsos and S. Mortensen. VESO Oslo. Norway

Keywords: interactions, Virulence, wildlife diseases, Atlantic salmon, transmission, Virus Diseases

Conference: AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.

Presentation Type: Oral

Topic: Aquatic Animal Epidemiology

Citation: Garseth A, Biering E and Skorping A (2016). Health monitoring in wild anadromous salmonids -Evidence of absence or absence of evidence?. Front. Vet. Sci. Conference Abstract: AquaEpi I - 2016. doi: 10.3389/conf.FVETS.2016.02.00037

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Received: 30 May 2016; Published Online: 14 Sep 2016.

* Correspondence: DVM, PhD. Ase Helen Garseth, Norwegian Veterinary Institute, Section for Environmental and Biosecurity Measures, Trondheim, NO-7485, Norway, ase-helen.garseth@vetinst.no