The native range of Gyrodactylus salaris expands from the Baltic sea to the Karelian isthmus in Russia. Gyrodactylus salaris has also been introduced to the rivers surrounding the Baltic sea to the North, and northern Europe.
Biogeographic Regions: palearctic (Introduced , Native )
Gyrodactylus salaris is a 0.5-1.0 mm long flat worm. As a monogean worm the dorsal side is usually convex and the ventral side concave. A monogean has three body regions: cephalic (anterior to pharynx) trunk (body) and penduncle (tapered end of body). This worm attaches to its host with an opisthaptor, which is an organ in the posterior region. Although usually colorless or grey, eggs or ingested food inside may make the worm appear red, pink, brown, yellow or black. Gyrodactylus salaris is hermaphroditic. Reproductively, it has an ovovitellarium, a fused mass of ova and vitelline cells. This species does not contain a vaginae, but has a birth pore.
All Gyrodactylus are essentially morphologically similar so they distinguish them by chaetotaxy and ribosomal RNA subunits as well as RNA internal transcribed spacers. Gyrodactylus salaris can be determined by using the oligonucleotide probe (GsV4) by performing polymerase chain reactions or PCR.
Average mass: 0.00025 g.
Range length: 0.5 to 1 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
As an ectoparasite on fish, Gyrodactylus salaris is found in freshwater. While it infects fish that migrate to and from the ocean, G. salaris is intolerant of full strength seawater. It has been postulated that G. salaris is a coldwater adapted parasite. If G. salaris is not attached to a host, it is not parasitic and floats on the bottom sediment or anywhere in the water column, hoping to come into contact with a host.
Habitat Regions: temperate ; polar ; freshwater
Aquatic Biomes: pelagic ; benthic ; lakes and ponds; rivers and streams; coastal
Other Habitat Features: intertidal or littoral
The adult stage of Gyrodactylus salaris feeds on the host’s skin, mucus, and fins. When they develop in their parent they receive nutrients from their parent as they develop into an adult.
Animal Foods: fish; body fluids
Primary Diet: carnivore (Piscivore , Eats body fluids)
Gyrodactylus salaris is a parasite of freshwater fish and fish migrating from the ocean to and from freshwater. It is found on the skin and fins of Atlantic Salmon, Salmo salar, rainbow trout Oncorhynchus mykiss, Arctic char Salvelinus alpinus, North American brook trout S. fontinalis, grayling Thymallus thymallus, North American lake trout Salvelinus namaycush, common whitefish Coregonus lavaretus, three-spined stickleback Gasterosteus aculeatus, common minnow Phoxinus phoxinus, ninespine Stickleback Pungitius pungitius, Solin Salmon Salmo obtusirostris, and brown trout Salmo trutta in their freshwater stage. They prefer to attach to the dorsal fin, pectoral fin, and anal fins in this sequential order. However, with increased density of Gyrodactylus salaris they are less selective and will attach to any area of open skin.
The disease resulting from its infections is gyrodactylosis, which has been reported to be responsible for the death of a wide variety of fish. Whatever the pathogenic mechanisms involved in gyrodactylosis are not known, but host mortality is probably due to the parasite.
Gyrodactylus salaris only feeds upon their hosts and do not affect the ecosystem in any other way except if they reduce their host's population.
Ecosystem Impact: parasite
Species Used as Host:
- Atlantic salmon, Salmo salar
- Rainbow trout, Oncorhynchus mykiss
- Arctic char, Salvelinus alpinus
- North American brook trout, Salvelinus fontinalis
- Grayling, Thymallus thymallus
- North American lake trout, Salvelinus namaycush
- Brown trout, Salmo trutta
- Common whitefish, Coregonus lavaretus
- Three-spined stickleback, Gasterosteus aculeatus
- Common minnow, Phoxinus phoxinus
- Ninespine stickleback, Pungitius pungitius
- Solin salmon, Salmo obtusirostris
Gyrodactylus salaris has no known predators and is difficult to control.
Life History and Behavior
Monogeans in general have a cerebral ganglia at the anterior end, and the nervous system extends out in a ladder pattern. This species likely has chemosensors and mechanosensors.
Communication Channels: chemical
Perception Channels: tactile ; chemical
All G. salaris are viviparous with embryos already containing a further developing embryo. These parasites have a specific birthing process of two daughters. The first daughter is created asexually from a ball of cells within the parent and then is released through the birth pore. The second daughter and all subsequent daughters develop from an oocyte and enter the uterus after the previous daughter is born. After the second daughter is born the male reproductive system become fully functional within the parent. All nutrition given to the developing oocyte is given through the uterus. They also do not have an egg shell that is normally created by vitelline cells. It is not known what exactly causes the birthing process, but after the birth of the daughter, she remains stationary while the mother moves to the anterior part of the host, most likely to ensure that there is no fertilization between mother and daughter. Once born, the parasite functions as an adult attaching to the same host as the parent and produces offspring 24 hours after its birth. In summary, every individual develops within its parent with no intermediate stage and is a fully functional adult upon birth.
The lifespan of Gyrodactylus salaris is temperature dependent. In colder temperatures it can attach to a dead host and survive to over 15 days. If not on a host the survival time is cut to 6 days.
Status: captivity: 6 to 15 days.
Status: captivity: 6 to 15 days.
Gyrodactylus salaris can reproduce both asexually and sexually. This species tends to lean towards asexual reproduction when the population density is low and sexual reproduction when the population density is high. There is no concrete information on the location and defending of mates but their mating behavior depends on the population size.
Gyrodactylus salaris reproduces all year long. Reproduction is reduced in the winter due to a decreased activity of its fish hosts which decrease its transmission and its availability to resources. All newborns are at first female and develop their male genitals later on in life. The first born daughter is born 24 hours after the birth of their parent. Gyrodactylus salaris only produces one offspring at a time. All daughters develop the same as the second daughter. When sexual reproduction is chosen one individual pierces the body of another individual with its hook, it inserts its penis and uses spines to stabilize itself while the cross-fertilization occurs. It then uses the sperm as well its already developing embryo to create an offspring that is genetically different from both parents and in this way ensures genetic variance within a population.
Breeding interval: This species produces throughout the year.
Range gestation period: 24 (low) hours.
Average gestation period: 24 hours.
Range time to independence: 0 to 0 minutes.
Range age at sexual or reproductive maturity (female or asexual): 0 to 0 minutes.
Range age at sexual or reproductive maturity (male): 0 to 0 minutes.
Key Reproductive Features: year-round breeding ; sequential hermaphrodite (Protogynous ); sexual ; asexual ; fertilization (External , Internal ); viviparous ; sperm-storing
All parental care occurs while the daughter is developing in the parent. They receive nutrients and grow until they are born in which they are left to defend for themselves.
Parental Investment: no parental involvement; pre-fertilization (Provisioning); pre-hatching/birth (Provisioning)
Molecular Biology and Genetics
Barcode data: Gyrodactylus salaris
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Gyrodactylus salaris
Public Records: 112
Specimens with Barcodes: 112
Species With Barcodes: 1
Gyrodactylus salaris is a common parasite and is therefore not a species of concern.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Relevance to Humans and Ecosystems
Gyrodactylus salaris can affect humans negatively by drastically decreasing the amount of Atlantic salmon. In Norway, it is calculated that they lose around 20 million Euros per year. Therefore, it hurts the economic value of these fisheries as well as depleting available food sources.
Gyrodactylus salaris has no positive benefits for humans.
Gyrodactylus salaris is a small monogenean ectoparasite (about 0.5 mm long) which mainly lives on the skin of freshwater fish, especially Atlantic salmon. This species is a leech-like parasite that has been implicated in some diminution of Atlantic salmon populations in the Norwegian fjords. Its common name is Salmon Fluke. Other species that can be parasitized include rainbow trout, Arctic char, North American brook trout, grayling, North American lake trout and brown trout.
The parasite attaches to the fish by a large specialized posterior attachment organ, the haptor which has sixteen sharp hooks located around its margin. The parasite cannot be seen with the naked eye, but it can be seen with a hand held lens. 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 and the epidermis of the host fish can be damaged which allows secondary infections. 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.
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.
The parasite cannot survive in the high salinity of sea water, so the infection is not spread by the migration of fish. 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 River and Lærdalselva River, two rivers in Norway.
- C.Michael Hogan. 2011. Norwegian Sea. Encyclopedia of Earth. Eds. P.Saundry & C.J.Cleveland. National Council for Science and the Environment. Washington DC
- Mitchin, Dan. "Gyrodactylus salaris". DAISIE - europe-aliens.org. Retrieved 11 November 2010.
- Gyrodactylus salaris, Scotland.gov, accessed 11 November 2010
- "Do not spread salmon parasite Gyrodactylus salaris". Finnish Ministry of Agriculture and Forestry. Retrieved 11 November 2010.
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