Gyrodactylus salaris

Geographic Range

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. (Johnsen, 2009)


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. (FRS Marine Laboratory Aberdeen, 2004; GyroDb, 2007; Johnsen, 2009)

Physical Description

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. (Cunningham, et al., 1995a; Cunningham, et al., 1995b; Johnsen, 2009; Lindenstrom, et al., 2003; Roberts and Janovy, Jr, 2000)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    0.00025 g
    0.00 oz
  • Range length
    0.5 to 1 mm
    0.02 to 0.04 in


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. (Cable and Harris, 2002; Olstad, et al., 2006)


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. (Cable and Harris, 2002)

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. (Bakke, et al., 1992; Cable and Harris, 2002)

  • 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

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. (Cable and Harris, 2002; Olstad, et al., 2006)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • provisioning


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. (Olstad, et al., 2006)

  • Range lifespan
    Status: captivity
    6 to 15 days
  • Typical lifespan
    Status: captivity
    6 to 15 days


Gyrodactylus salaris is a social species. The amount of individuals in a population is based on the amount of available hosts, and has a very quick and devastating reproductive capability. It is able to slowly move around on the substrate in its aquatic environment and around its host by alternating between its opisthaptor and anterior adhesive organs, but is not able to maneuver in the open water. There are no social hierarchies within this species since its mode of reproduction is based on population density. (Bakke, et al., 1992; Paladini, et al., 2009)

Home Range

They do not have a defined home range since they can travel along with their hosts and can switch from hosts of different species that have different home ranges. (Bakke, et al., 1992)

Communication and Perception

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. (Roberts and Janovy, Jr, 2000)

Food Habits

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. (FRS Marine Laboratory Aberdeen, 2004)

  • Animal Foods
  • fish
  • body fluids


Gyrodactylus salaris has no known predators and is difficult to control.

Ecosystem Roles

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. (GyroDb, 2007; Harris, et al., 1998; Johnsen, 2009; Malmberg, 1973)

Species Used as Host

Economic Importance for Humans: Positive

Gyrodactylus salaris has no positive benefits for humans.

Economic Importance for Humans: Negative

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. (Cable, et al., 2000; FRS Marine Laboratory Aberdeen, 2004; Johnsen, 2009)

Conservation Status

Gyrodactylus salaris is a common parasite and is therefore not a species of concern.


Andrew Szczembara (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.



living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map


reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents


Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


an animal that mainly eats fish


the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.


condition of hermaphroditic animals (and plants) in which the female organs and their products appear before the male organs and their products


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year


Bakke, T., P. Harris, P. Jansen, L. Hansen. 1992. Host specificity and dispersal strategy in gyrodactylid monogeneans, with particular reference to Gyrodactylus salaris (Platyhelminthes, Monogenea). Diseases of Aquatic Organisms, 13: 63-74.

Cable, J., P. Harris. 2002. Gyrodactylid Developmental Biology: historical review, current status and future trends. International Journal for Parasitology, 32: 255-280.

Cable, J., P. Harris, T. Bakke. 2000. Population growth of Gyrodactylus salaris (Monogenea) on Norwegian and Baltic Atlantic salmon (Salmo salar) stocks. Parasitology, 121 (6): 621-629.

Cunningham, C., D. McGillivray, K. MacKenzie. 1995. Phylogenetic analysis of Gyrodactylus salaris Malmberg, 1957 based on the small subunit (18S) ribosomal RNA gene. Molecular and Biochemical Parasitology, 71 (1): 139-142.

Cunningham, C., D. McGillivray, K. MacKenzie, W. Melvin. 1995. Discrimination between Gyrodactylus salaris, G. derjavini and G. truttae (Platyhelminthes: Monogenea) using restriction fragment length polymorphisms and an oligonucleotide probe within the small subunit ribosomal RNA gene. Parasitology, 111: 87-94. Accessed March 19, 2011 at

FRS Marine Laboratory Aberdeen, 2004. "Gyrodactylus salaris" (On-line). Accessed March 19, 2011 at

GyroDb, 2007. "Gyrodactylus salaris" (On-line). GyroDb - A home for gyrodactylids on the web. Accessed March 19, 2011 at

Harris, P., A. Soleng, T. Bakke. 1998. Killing of Gyrodactylus salaris (Platyhelminthes, Monogenea) mediated by a host complement. Parasitology, 117 (2): 137-143.

Johnsen, B. 2009. "NOBANIS - Invasive Alien Species Fact Sheet Gyrodactylus salaris" (On-line). Accessed March 20, 2011 at

Lindenstrom, T., C. Collins, J. Bresciani, C. Cunningham, K. Buchmann. 2003. Characterization of a Gyrodactylus salaris variant: infection biology, morphology and molecular genetics. Parasitology, 127: 165-177. Accessed March 19, 2011 at

Malmberg, G. 1973. Gyrodactylus infestations on species of Salmo in Danish and Swedish hatcheries. Norwegian Journal of Zoology, 21: 325 - 326.

Olstad, K., J. Cable, G. Robertsen, T. BaCablekke. 2006. Unpredicted transmission strategy of Gyrodactylus salaris (Monogenea: Gyrodactylidae): Survival and infectivity of parasites on dead hosts. Parasitology, 133 (1): 33-41.

Paladini, G., A. Gustinelli, M. Fioravanti, H. Hansen, A. Shinn. 2009. First report of Gyrodactylus salaris Malmberg, 1957 (Platyhelminthes, Monogenea) on Italian cultured stocks of rainbow trout (Oncorhynchus mykiss Walbaum). Veterinary Parasitology, 165 (3-4): 290-297.

Roberts, L., J. Janovy, Jr. 2000. Foundations of Parasitology. Boston: McGraw Hill.