Gyrodactylus salaris

Gyrodactylus salaris
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Platyhelminthes
Class:	Monogenea
Order:	Gyrodactylidea
Family:	Gyrodactylidae
Genus:	Gyrodactylus
Species:	G. salaris
Binomial name
Gyrodactylus salaris Malmberg,1957

A warning sign in Scotland

Gyrodactylus salaris,commonly known assalmon fluke,salmon killer,or theNorwegian salmon killeris a tinymonogeneanectoparasitewhich lives on the body surface of freshwater fish.This leech-like parasite has been implicated in the reduction ofAtlantic salmonpopulations in theNorwegian fjords.It also parasitises other species, includingrainbow trout.G. salarisrequiresfresh water,but can survive inbrackish waterfor up to 18 hours.

The parasite is 0.5 mm (0.02 in) long,and cannot be seen with the naked eye, but it can be seen with amagnifying glass.On itsposteriorend is ahaptor,a specialized organ for attaching to the host fish, which has sixteen hooks around its edge.The parasite isviviparous,that is, it produces live offspring. 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.

Interactions with host fish

When feeding, the parasite attaches its anterior end to the fish with cephalic glands. It everts itspharynxthrough the mouth and releases a digestive solution withproteolytic enzymeswhich dissolves the salmon skin.Mucusand 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.

History

G. salariswas first described in 1952,after being removed from a Baltic strainof Atlantic salmon kept at the Hölle Laboratory in Sweden, near to the river Indalsälv.At the time, it was not thought to cause disease in the host fish.The presence ofG. salarison fish became aWorld Organisation for Animal Healthnotifiable disease in 1983.

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

Historically,Gyrodactylus-infected rivers have been treated with the indiscriminate pesticide/pisciciderotenone.A newer method of treatment employs dosing small volumes of aqueousaluminiumandsulfuric acidinto 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 inBatnfjordelvaand Lærdalselva, two rivers inNorway.