Gyrodactylus salaris
Gyrodactylus salaris.png
Scientific classification edit
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Monogenea
Order: Gyrodactylidea
Family: Gyrodactylidae
Genus: Gyrodactylus
G. salaris
Binomial name
Gyrodactylus salaris
Malmberg, 1957
A warning sign in Scotland
A warning sign in Scotland

Gyrodactylus salaris, commonly known as salmon fluke,[1] is a tiny monogenean ectoparasite which lives on the body surface of freshwater fish.[2] This leech-like parasite has been implicated in the reduction of Atlantic salmon populations in the Norwegian fjords.[3] It also parasitises other species, including rainbow trout.[4] G. salaris requires fresh water,[2] but can survive in brackish water for up to 18 hours.[5]

The parasite is 0.5 mm (0.02 in) long,[2] and cannot be seen with the naked eye, but it can be seen with a magnifying glass.[6] On its posterior end is a haptor, a specialized organ for attaching to the host fish, which has sixteen hooks around its edge.[2] The parasite is viviparous, that is, it produces live offspring.[7] The parasites give birth to live young nearly as big as themselves and at this time, a further generation is already growing inside the neonates.[4]

Interactions with host fish

When feeding, the parasite attaches its anterior end to the fish with cephalic glands. It everts its pharynx through the mouth and releases a digestive solution with proteolytic enzymes which dissolves the salmon skin. Mucus and dissolved skin are then sucked into the gut. Attachment of many parasites can cause large wounds, damaging the epidermis of the host fish, which allows secondary infections.[4]


G. salaris was first described in 1952,[8] after being removed from a Baltic strain[2] of Atlantic salmon kept at the Hölle Laboratory in Sweden, near to the river Indalsälv.[8] At the time, it was not thought to cause disease in the host fish.[8] The presence of G. salaris on fish became a World Organisation for Animal Health notifiable disease in 1983.[8]

Catastrophic losses of Atlantic salmon occurred in Norway in the 1970s following the introduction of G. salaris. By 2001, the salmon populations of 41 Norwegian rivers had been virtually wiped out in this way.[4]

Historically, Gyrodactylus-infected rivers have been treated with the indiscriminate pesticide/piscicide rotenone. A newer method of treatment employs dosing small volumes of aqueous aluminium and sulfuric acid into the river. A huge advantage of this method is its ability to kill the parasites without harming the hosts. This new method has shown promising results in Batnfjordelva and Lærdalselva, two rivers in Norway.[9]


  1. ^ Minchin, Dan (7 January 2008). "Gyrodactylus salaris" (PDF). DASIE: Delivering Alien Invasive Species Inventories for Europe. Archived from the original (PDF) on 24 December 2017. Retrieved 2017-11-05.
  2. ^ a b c d e Cain, Kenneth D.; Polinski, Mark P. (2014). "Chapter 3. Infectious diseases of coldwater fish in fresh water. Gyrodactylosis". In Woo, Patrick T.K.; Bruno, David W. (eds.). Diseases and disorders of finfish in cage culture (2nd ed.). CABI. pp. 95–96. ISBN 9781780642079.
  3. ^ C.Michael Hogan. 2011. Norwegian Sea. Encyclopedia of Earth. Eds. P.Saundry & C.J.Cleveland. National Council for Science and the Environment. Washington DC
  4. ^ a b c d "Notifiable diseases : Gyrodactylus salaris". Scottish Government. 8 December 2009. Retrieved 2017-11-05.
  5. ^ Hopkins, CCE (2002). "Introduced marine organisms in Norwegian waters, including Svalbard. Parasites and diseases". In Leppäkoski, Erkki; Gollasch, Stephan; Olenin, Sergej (eds.). Invasive Aquatic Species of Europe. Distribution, Impacts and Management. Dordrecht: Springer Netherlands. pp. 251–252. ISBN 9789401599566.
  6. ^ "Do not spread salmon parasite Gyrodactylus salaris" (PDF). Finnish Ministry of Agriculture and Forestry. Archived from the original (PDF) on 30 August 2005. Retrieved 11 November 2010.
  7. ^ Shoemaker, Craig; Xu, De-Hai; LaFrentz, Benjamin; LaPatra, Scott (2015). "Chapter 1: Overview of fish immune system and infectious diseases. Monogenetic trematodes". In Lee, Cheng-Sheng; Lim, Chhorn; Gatlin, Delbert M. III; Webster, Carl D. (eds.). Dietary Nutrients, Additives, and Fish Health. Wiley-Blackwell. p. 16. ISBN 978-0-470-96288-6.
  8. ^ a b c d Harris, Phil D.; Bachmann, Lutz; Bakke, Tor A. (2011). "The parasites and pathogens of the Atlantic salmon: Lessons from Gyrodactylus salaris". In Aas, Øystein; Klemetsen, Anders; Einum, Sigurd; Skurdal, Jostein (eds.). Atlantic Salmon Ecology. John Wiley & Sons. pp. 221–244. ISBN 9781444348194.
  9. ^ Robinson JV, James AL (1975). "Some observations on the effects produced in white mice following the injection of certain suspensions of corroding bacilli". Br J Exp Pathol. 56 (1): 14–6. PMC 2072709. PMID 1080.