Anisakis simplex

Geographic Range

Anisakis simplex has a wide range of hosts throughout its life cycle and an equally large geographic range. This parasitic worm can be found in crustaceans, squid, fish, and marine mammals in oceans and seas from the tropics to the arctic and antarctic regions. (Bullini, 1997; Oliva, 1999)


The immediate habitat of Anisakis simplex is inside the hemocoel of its crustacean intermediate host where the parasite develops into its third stage juvenile. Generally it is inside the gut of its paratenic and definitive hosts as a third stage juvenile and adult respectively. Second stage juveniles are able to live freely in sea water until becoming ingested by a crustacean.

The more indirect habitat of A. simplex is the marine environment where its hosts live. (Karasev, 1993)

Physical Description

Members of the Phylum Nematoda are wormlike, have a pseudocoel and complete digestive system. Their bodies are covered with a non-cellular cuticle composed of collagen and other compounds which is secreted by the epidermis. The cuticle has three main layers and is shed four times throughout their life cycle. The nematode psuedocoel, filled with fluid, functions as a hydrostatic skeleton. Somatic musculature, composed of longitudinal muscles, acts against the stretching and compression of the cuticle to produce movement. Connected to the main body of muscles are dorsal and ventral longitudinal nerve cords.

Like most other ascaridid nematodes, A. simplex possesses three protruding lips around its mouth opening. These lips are poorly developed in juvenile stages, but contain inner labial papillae, which may function as combined chemomechanosensory receptors in adults. Male ascaridids possess simple spicules used to hold the female genital pore open against hydrostatic pressure during copulation.

Anisakis simplex juveniles range in size from less than 5 mm as second stage juveniles to more than 30 mm in their fourth stage. (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000; Smith, 1983)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    5 to 30 mm
    0.20 to 1.18 in


The life cycle of A. simplex begins when eggs are passed through the feces of its definitive host. The definitive hosts of this species include many marine mammals such as whales, porpoises, and seals. Once the eggs are passed, they hatch into second stage juveniles. The juveniles must be consumed by an intermediate host, usually a euphausiid crustacean, for the life cycle to continue. Physical changes to the environment that are specific to the hemocoel of the crustacean probably signals the worms to develop into a third stage juvenile. Predators of crustaceans, usually fish or squid, become infected by A. simplex after eating an infected crustacean. Because A. simplex does not undergo any development inside the gut of the fish or squid, these predators are considered paratenic hosts of the nematode. The life cycle is completed after the paratenic host is ingested by a definitive host. Inside its final mammalian host, the worm develops into a sexually mature adult. Because A. simplex eggs are shed from the host throughout the year, they may develop and hatch at any time, thus acquisition of infection by hosts is non-seasonal.

While the above mentioned life cycle is accepted by many scientists, there is considerable evidence that two molts actually occur during development in the egg of A. simplex and that it is the third stage juvenile which hatches from the egg. (Koie, 1995; Podolska, 1995; Roberts and Janovy, 2000; Smith, 1983)


Inside its final mammalian host, the worm develops into a sexually mature adult. Females may produce a pheromone to attract males. The male coils around a female with his curved area over the female genital pore. The gubernaculum, made of cuticle tissue, guides spicules which extend through the cloaca and anus. Males use spicules to hold the females during copulation. Nematode sperm are amoeboid-like and lack flagella. (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000; Smith, 1983)

  • Parental Investment
  • pre-fertilization
    • provisioning


Nematodes such as Anisakis simplex swim intermittently. The worms are usually only able to move effectively when the pseudocoel is filled with fluid and hypertonic to the surrounding media. (Barnes, 1987; Brusca and Brusca, 2003)

Communication and Perception

Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.

Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors). (Barnes, 1987; Brusca and Brusca, 2003)

Food Habits

Like other ascaridid nematodes, Anisakis simplex feeds on the gut contents of its definitive host as an adult. Pharyngeal glands and intestinal epithelium produce digestive enzymes. Extracellular digestion begins within the lumen and is finished intracellularly. (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000)

  • Animal Foods
  • body fluids


These parasites are usually not preyed on directly, but are ingested from host to host. Larval mortality is high due to its inability to reach a suitable host. (Barnes, 1987; Brusca and Brusca, 2003)

Ecosystem Roles

This parasitic worm can be found in crustaceans, squid, fish, and marine mammals in oceans and seas from the tropics to the arctic and antarctic regions.

Species Used as Host

Economic Importance for Humans: Negative

Anisakis simplex is of much medical importance because of the severe allergic reactions and gastrointestinal symptoms it causes in humans after eating or handling infected fish or crustaceans. These reactions include chronic uticaria (skin rashes), gastric ulcers, and anaphylaxis (a hyper-immune response). These symptoms are termed anisakiasis and are especially prevalent in countries where it is common to eat raw or undercooked fish. Populations of fishermen are also at risk of developing anisakiasis as well as developing occupational asthma caused by the inhalation of antigens from A. simplex. However, even people who take special precautions when handling and preparing their fish are at risk of developing anisakiasis. It has been reported that A. simplex can survive at temperatures of over 65 degrees Celsius inside a microwave oven. (Adams, et al., 1999; Armentia, 1998; Moreno-Ancillo, et al., 1997; Purello-D'Ambrosio, et al., 2000)


Renee Sherman Mulcrone (editor).

Julie Ritter (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.


Arctic Ocean

the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map


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 southern part of the New World. In other words, Central and South America.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map


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

World Map


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.

brackish water

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


an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).


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


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.


union of egg and spermatozoan


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.


having the capacity to move from one place to another.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.


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


chemicals released into air or water that are detected by and responded to by other animals of the same species


structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.


remains in the same area


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


uses touch to communicate


Adams, A., K. Miller, M. Wekell, F. Dong. 1999. Survival of Anisakis simplex in microwave-processed arrowtooth flounder (Atheresthes stomias). Journal of Food Protection, 62 (4): 403-409.

Armentia, A. 1998. Occupational asthma by Anisakis simplex. Journal of Allergy & Clinical Immunology, 102 (5): 831-834.

Barnes, R. 1987. Invertebrate Zoology. Orlando, Florida: Dryden Press.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Bullini, L. 1997. Antarctic Communities: Species, Structure, and Survival. UK: Cambridge University Press.

Center for Food Safety & Applied Nutrition, 2003. "Anisakis simplex and related worms" (On-line). Bad Bug Book. Accessed September 14, 2004 at

Karasev, A. 1993. Parasitological Studies of Northern Basin Fish. Russia: Pinro, Murmansk.

Koie, M. 1995. Development to third stage larvae occurs in the eggs of Anisakis simplex and Pseudoterranova decipiens. Candian Journal of Fisheries and Aquatic Sciences, 52: 134-139.

Moreno-Ancillo, A., M. Caballero, R. Cabanas, J. Contreras, J. Martin-Barroso. 1997. Allergic reactions to Anisakis simplex parasitizing seafood. Annals of Allergy, Asthma, & Immunology, 79 (3): 246-250.

Ohio State University, 2001?. "Anistakis spp." (On-line). Parasites and Parasitological Resources. Accessed September 15, 2004 at

Oliva, M. 1999. Metazoan parasites of the jack mackerel Trachurus murphyi in a latitudinal gradient from South America (Chile and Peru). Parasite, 6 (3): 223-230.

Podolska, M. 1995. The role of cod (Gadus morhua) in the life-cycle of Anisakis simplex in the southern Baltic Sea. Scientific Papers Presented at the Polish-Swedish Symposium on Baltic Cod, No. 327: 115-122.

Purello-D'Ambrosio, F., E. Pastorello, S. Gangemi, G. Lombardo, L. Ricciardi. 2000. Incidence of sensitivity to Anisakis simplex in a risk population of fishermen/fishermongers. Annals of Allergy, Asthma, & Immunology, 84 (4): 439-444.

Roberts, L., J. Janovy. 2000. Foundations of Parasitology: Sixth Edition. Boston: McGraw-Hill Higher Education.

Smith, J. 1983. Anisakis simplex: Morphology and morphometry of larvae from euphausiids and fish, and a review of the life-history and ecology. Journal of Helminthology, 57 (3): 205-224.