Argulus foliaceus

Geographic Range

Argulus foliaceus is a freshwater fish ectoparasite that has been reported throughout temperate regions of Europe, Central Asia, and North America. It has been well studied in Europe, especially the British Isles, where is has had major impacts on UK sport fisheries through fish stress and mortality. (Harrison, et al., 2006; Oktener, et al., 2007; Pasternak, et al., 2004)


Argulus foliaceus is found in warm, eutrophic, still lakes of both fresh and brackish water. Eggs are laid in shady areas, rather than in direct sunlight. Typically considered a shallow water species, this louse is often observed laying eggs within the top 1 m of the water column (although it will lay eggs in deeper water at the end of the reproductive season). Argulus foliaceus is an obligate parasite, requiring host availability. This louse has a low host specificity, so it can infect a variety of fish within its habitat. (Harrison, et al., 2006; Pasternak, et al., 2000; Taylor, et al., 2006)

Physical Description

On average, Argulus foliaceus measures a total length of 3-7 mm and a width of 2.5-5 mm. Argulid females are generally larger than males, and the growth of the parasite may be influenced by the size of the host. A distinguishing characteristic of A. foliaceus is the urosome, consisting of rounded lobes that are covered marginally with small spines. The posterior incisures of the urosome do not reach to the center. Another characteristic is the anterior portion of the cephalothorax that forms a broad protrusion with shallow grooves. Adults use suction discs for host attachment, whereas larvae utilize larval hooks. (Moller, et al., 2008; Oktener, et al., 2007; Pasternak, et al., 2004)

  • Sexual Dimorphism
  • female larger
  • Range length
    3 to 7 mm
    0.12 to 0.28 in


Argulus foliaceus larvae are free-swimming. The length of the larval phase is highly variable, most likely influenced by temperature. In general, larvae are typically first observed in the late spring and morph into adults in the fall. Argulus foliaceus is exceedingly rare in the winter. Larval development is divided into two distinct morphological phases: stage I as a metanauplius and stage two as a juvenile. While morphological adaptations do appear in stage I larvae, there is currently no conclusive evidence that the stage I larvae are either parasitic or pelagic, so they are typically considered “semi-pelagic." (Moller, et al., 2007; Pasternak, et al., 2000)


Argulus foliaceus usually copulates on the surface of a host fish, but copulation has also been observed on other types of solid surfaces such as leaves and stones. (Pasternak, et al., 2000)

A female A. foliaceus leaves the host fish to lay its eggs, but as an obligate parasite, it must return to a host fish occasionally throughout the process. There is variability in the frequency and length of time that the female leaves and returns to the host. Because females are dependent on the host fish while laying eggs, the individual vulnerability and population density of fish can influence this louse's reproductive success and survivorship. While A. foliaceus is commonly believed to be a shallow water species because it is most often observed to lay eggs in the top 1 m of the water column, some studies have indicated that, if available, they prefer deeper water (8.5 m) at the end of the egg-laying season. The suggestion that they lay eggs in shallow water may be a bias due to study sites. Temperature and dissolved oxygen content may influence egg laying depths, but there is currently no conclusive evidence for these trends. Eggs are laid in strings or clutches that contain an average of 100-150 eggs, but there can be as few as four or as many as 250 eggs. The female lays her eggs in the winter, but there is a wide variability in hatching time, possibly due to fish availability. (Harrison, et al., 2006; Pasternak, et al., 2000)

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • oviparous
  • Breeding season
    Eggs laid in the winter
  • Range number of offspring
    4 to 250
  • Average number of offspring

There is no information about parental investment in Argulus foliaceus reported in the literature.

  • Parental Investment
  • no parental involvement


Argulus foliaceus is rare in the winter and has been described as having a short lifespan. There is no information reported in the literature, however, on the actual length of its lifespan. (Dzika, 2002; Pasternak, et al., 2000)


Argulus foliaceus most commonly attaches to the host on the skin epithelium of the body and fins, but has been observed to also attach to the gills. This louse feeds by piercing the host skin, injecting a toxin, and drawing blood. Infection of A. foliaceus often results in host tissue damage and sometimes mortality. Argulus foliaceus infects irrespective of the health of the host. The length of residence time on the host between attachment to detachment is quite variable. In general, ectoparasites aggregate on the host so that few individuals within the host population are actually infected. The aggregation is likely due to host behavior; when stressed, the host’s movement is reduced, allowing more parasites to attach. (Bandilla, et al., 2005; Nolan, et al., 2000; Oktener, et al., 2006; Pasternak, et al., 2004)

Home Range

There is no information on the home range of Argulus foliaceus reported in the literature.

Communication and Perception

Adult argulids can respond to some chemical cues. They have higher sensory abilities, swimming abilities, and metabolism than juveniles, so the adults are less dependent on host attachment, allowing them to leave one host in search for another of higher preference. At the individual level, the searching abilities of Argulus foliaceus are limited, so changes at the population level, such as host preference and aggregation, are necessary to increase reproductive success and survivorship, in light of unpredictable host availability. (Bandilla, et al., 2005; Pasternak, et al., 2000)

Food Habits

Argulus foliaceus is an obligate bloodsucker, and it cannot survive more than few days without a host. Having little specificity for hosts, it infects a wide range of species. (Pasternak, et al., 2000)

  • Animal Foods
  • amphibians
  • fish


Direct predation of free-swimming Argulus foliaceus by trout and some other fish species has been observed. (Taylor, et al., 2006)

  • Known Predators
    • Trout

Ecosystem Roles

Argulus foliaceus is often noted for its role in ecosystems as an ectoparasite. With a low host specificity, it has been found on almost every type of freshwater fish within its natural habitat, yet some fish are more susceptible than others. Argulus foliaceus has been reported on fish in the families Cyprinidae, Salmonidae, Gobiidae, Gasterosteidae, and Acipenseridae, as well as amphibians, including frogs and toads (Anura). In fish farms of Central Finland, it was found to coexist with Argulus coregoni, a closely related ectoparasite. In addition to its function in ecosystems as a parasite, A. foliaceus can also be a vector for bacteria and flagellates, and it serves as an intermediate host of nematodes in the family Skrjabillanidae. (Oktener, et al., 2006; Pasternak, et al., 2004; Walker, et al., 2007)

Commensal/Parasitic Species
  • Skrjabillanidae

Economic Importance for Humans: Positive

There are no known positive effects of Argulus foliaceus on humans.

Economic Importance for Humans: Negative

While Argulus foliaceus is frequently found in small numbers with little damage to the hosts, epizootics may occur. When infected by A. foliaceus, host fish display an increase in jumping behavior and a decrease in feeding, followed by secondary bacterial and fungal infections, shoaling behavior, and finally, possible large-scale mortality. Argulus foliaceus infections have been reported to wipe out trout stock populations and cause problems in carp farming. In sport fisheries, a common issue is not mortality but rather reduced catch and lowered aesthetic appeal, resulting in economic losses. (Cross and Stott, 1974; Nolan, et al., 2000; Taylor, et al., 2006)

Conservation Status

Other Comments

Argulus foliaceus is a mechanical vector of the spring viraemia of carp (SVC), an acute viral disease in Cyprinus carpio, transferring the virus from infected to non-infected individuals. (Ahne, 1985)


Jessica Kafer (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Renee Mulcrone (editor), Special Projects.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


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

World Map

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.

brackish water

areas with salty water, usually in coastal marshes and estuaries.


an animal that mainly eats meat


uses smells or other chemicals to communicate


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


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.


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.


specialized for swimming


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


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


an animal that mainly eats blood


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


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).


Ahne, W. 1985. Argulus foliaceus L. and Piscicola geometra L. as mechanical vectors of spring viraemia of carp virus (SVCV). Journal of Fish Diseases, 8: 241-242.

Bandilla, M., T. Hakalahti, P. Hudson, E. Valtonen. 2005. Aggregation of Argulus coregoni (Crustacea: Branchiura) on rainbow trout (Oncorhynchus mykiss): a consequence of host susceptibility or exposure?. Parasitology, 130: 1-8. Accessed March 02, 2011 at

Cross, D., R. Stott. 1974. The effect of Argulus foliaceus L. on the growth and mortality of a grass carp population. Fisheries Management, 5: 39-42.

Dzika, E. 2002. The parasites of bream Abramis brama (L.) from Lake Kortowskie. Archives of Polish Fisheries, 10: 85-96. Accessed March 02, 2011 at

Harrison, A., N. Gault, J. Dick. 2006. Seasonal and vertical patterns of egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea: Branchiura). Diseases of Aquatic Organisms, 68: 167-173. Accessed March 02, 2011 at

Moller, O., J. Olesen, A. Avenant-Oldewage, P. Thomsen, H. Glenner. 2008. First maxillae suction discs in Branchiura (Crustacea): development and evolution in light of the first molecular phylogeny of Branchiura, Pentastomida, and other "Maxillopoda". Arthropod Structure & Development, 37: 333-346. Accessed March 02, 2011 at

Moller, O., J. Olesen, D. Waloszek. 2007. Swimming and cleaning in the free-swimming phase of Argulus larvae (Crustacea, Branchiura) - appendage adaptation and functional morphology. Journal of Morphology, 268: 1-11. Accessed March 02, 2011 at,%20Olesen,%20Waloszek%202007.pdf.

Nolan, D., A. van der Salm, S. Wendelaar Bonga. 2000. The host-parasite relationship between the rainbow trout (Oncorhynchus mykiss) and the ectoparasite Argulus foliaceus (Crustacea: Branchiura): epithelial mucous cell response, cortisol and factors which may influence parasite estalishment. Contributions to Zoology, 69: 57-63. Accessed March 02, 2011 at

Oktener, A., A. Ali, A. Gustinelli, M. Fioravanti. 2006. New host records for fish louse Argulus foliaceus L., 1758 (Crustacea, Branchiura) in Turkey. Ittiopatologia, 3: 161-167.

Oktener, A., J. Trilles, I. Leonardos. 2007. Five ectoparasites from Turkish fish. Turkiye Parazitologi Dergisi, 31: 154-157. Accessed March 02, 2011 at

Pasternak, A., V. Mikheev, E. Valtonen. 2004. Growth and development of Argulus coregoni (Crustacea: Branchiura) on salmonid and cyprinid hosts. Diseases of Aquatic Organisms, 58: 203-207. Accessed March 02, 2011 at

Pasternak, A., V. Mikheev, E. Valtonen. 2000. Life history characteristics of Argulus foliaceus L. (Crustacea: Branchiura) populations in Central Finland. Annales Zoologici Fennici, 37: 25-35. Accessed March 02, 2011 at

Taylor, N., C. Sommerville, R. Wootten. 2006. The epidemiology of Argulus spp. (Crustacea: Branchiura) infections in stillwater trout fisheries. Journal of Fish Diseases, 29: 193-200.

Walker, P., J. Harris, G. van der Velde, S. Bonga. 2007. Size matters: stickleback size and infection with Argulus foliaceus (L., 1758) (Branchiura, Arguloida). Crustaceana, 80: 1397-1401.