Triaenophorus crassus

Geographic Range

Triaenophorus crassus is present in the Neartic Region and the Palearctic Region. Specific countries thid parasite has been found in are: Austria, Sweden, Denmark, Finland, Norway, Canada, Switzerland, Bulgaria, Slovakia, Germany and the United States. (Achleitner, et al., 2009; Ekbaum, 1935; Ondrackova, et al., 2005; Ondrackova, et al., 2006; Pulkkinen, et al., 1999; Pulkkinen, et al., 2000)


Triaenophorus crassus is the pike tapeworm, so the habitat is aquatic. This species is also restricted to fresh bodies of water that are home to the pike. The coracidium stage of its lifecycle is free swimming for 1-2 days. The procercoid’s habitat is inside a copepod’s hemocoel (body cavity). The adult lives in the intestine of the pike. ("Triaenophorus crassus", 2000; Miller, R.B., 1952; Wardle, et al., 1974)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Triaenophorus crassus is larger and thicker than similar tapeworms of its class. The body is divided into three sections: the scolex, which is the anchoring structure, the neck and the strobila. As an adult it is the only pseudophyllidean that has hooks on the scolex and the four hooks are tri-dentate. Triaenophorus crassus also has bothria, the dorsal and ventral grooves running down the length of the scolex. The strobila is made up of individual segments, or proglottids. The internal segmentation has no clearly defining external margins to the proglottids. Proglottids contain both the male and female reproductive structures, and are self-fertilizing. The genital pore is located on the side of each proglottid alternating sides. The cirrus sac extends centrally to the midline of the body. The female system includes the uterus, ovary, ootype, seminal vesicle, and vitellaria. Above the cirrus sac is a small uterus that normally contains the eggs. Above the uterus are numerous large circular testes, and small circular vitellaria. Below the cirrous sac, there is a small bilobed ovary, and below that is Mehils' gland. The visible internal structures include both the female and male reproductive structures. The male system contains testes, and the vas efferens, vas deferens system that terminates in the cirrous pouch containing the cirrous sac. ("Triaenophorus crassus", 2000; Ekbaum, 1935; Pulkkinen, et al., 2000)


Triaenophorus crassus needs three hosts during its life cycle. Eggs are released from the adult into the water. After the eggs hatch in 1-2 weeks, a free swimming ciliated coracidium emerges. The coracidium swims for 1-2 days, and needs to be consumed by its next host, a copepod. Once ingested by a copepod the parasite migrates to the hemocoel and develops into a procercoid. The copepod is then eaten by a whitefish and digested. As it is being digested it penetrates the gut wall and enters the fish musculature. Here the parasite may migrate for up to several months. During this time the parasite becomes a plercocercoid larva and acquires hooks. When the whitefish is eaten by the definitive host (a pike) the parasite attaches to the intestine where it matures to adulthood. During the spawning time of the pike, a short period in the spring, adult T. crassus release its scolex from the pike. As the entire animal reaches the water, it releases eggs in littoral areas. ("Triaenophorus crassus", 2000; Pulkkinen, et al., 1999; Pulkkinen, et al., 2000)


Triaenophorus crassus reproduction is limited to littoral areas, during a short period in the spring. This is convergent to the spawning season of the pike. The tapeworm is hermaphroditic. The proglottids continue to grow from the scolex producing a chain. The proglottids mature and since they contain both male and female reproductive organs they self-fertilize. The last segment of the chain breaks off and the eggs are passed out as the pike are spawning. (Pulkkinen, et al., 1999)

Triaenophorus crassus can reproduce on its own. The proglottid contains both male and female reproductive organs facing to the opposite sides. The tapeworm reproduces by laying eggs that are released through the genital pore when the adult cestode comes in contact with water as it exits the fish during spawning. One adult can release more than one million eggs. The hatching time of the eggs is highly variable increasing the success of reproduction. (Achleitner, et al., 2009; "Triaenophorus crassus", 2000; Pulkkinen, et al., 1999)

  • Breeding interval
    This tapeworm breeds once yearly.
  • Breeding season
    The breeding season is coordinated at the same time as the pikes, which is early spring.

Triaenophorus crassus releases eggs but has no further parental investment. (Lahnstein, et al., 2009; Miller, R.B., 1952)

  • Parental Investment
  • no parental involvement


The lifespan of Triaenophorus crassus is several years. (Achleitner, et al., 2009)


Triaenophorus crassus is a fish intestine tapeworm, therefore it’s behavior is parasitic. Through each step in the life cycle after the eggs hatch, it is eaten and then it uses the host’s resources for development. (Vickova, et al., 2007)

Home Range

The home range for the adult is the intestine of the pike. (Uzmann and Hesselholt, 1957)

Communication and Perception

There are no studies on the communication and perception abilities of Triaenophorus crassus.

Food Habits

Triaenophorus crassus is an intestinal tape worm, therefore it obtains its food by absorption from the intestine of the host. The task of attaching to the intestine is done by the scolex and the hooks located on this structure. The main food sources are carbohydrates, glucose and other mono and polysaccharides. (Arme and Pappas, 1983; Southwell, 1930)

  • Animal Foods
  • body fluids


Triaenophorus crassus has no known predators.

Ecosystem Roles

Triaenophorus crassus has been shown have an effect on the surrounding ecosystem. The first intermediate hosts of the parasite are the copepods. Copepods infected with 12-days old or older procercoids, have shown a parasite induced change in their swimming behavior. Instead of swimming close to the bottom which is characteristic of healthy copepods, infected individuals approached the water surface. Triaenophorus crassus affects its surrounding ecosystem by altering the behavior of the copepods, causing them to be more susceptible to predation by the whitefish. (Pulkkinen, et al., 2000)

Species Used as Host

Economic Importance for Humans: Positive

Triaenophorus crassus, as a parasite species has not been shown to have any positive economic importance.

Economic Importance for Humans: Negative

The negative affect of Triaenophorus crassus is that the second intermediate host, which are the whitefish or the ciscoes show a physical development of cysts as a direct consequence of being infested. An accumulation of these cysts can render the fish unmarketable. The cysts are actually harmless to mammals, but they cause the fish to be objectionable in appearance and therefore undesirable. The whitefish are a popular choice for consumers and this parasite infection results in loss of profit for the fishing industry. (Miller, R.B., 1952; Wardle, et al., 1974)

Conservation Status

There have not been any actions taken to conserve Triaenophorus crassus. The main focus has been directed towards population control and eradication. (Miller, R.B., 1952)


Zsuzsanna Szabo (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 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.


an animal that mainly eats meat


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


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.


a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

internal fertilization

fertilization takes place within the female's body


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.


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

seasonal breeding

breeding is confined to a particular season


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).


Department of Zoology, University of Manitoba. 2000. "Triaenophorus crassus" (On-line). Accessed March 23, 2011 at

Achleitner, D., H. Gassner, R. Schabetsberger. 2009. 'Global Worming': first record of an epidemic of Triaenophrus crassus in a population of Arctic charr, Salvelinus umbla. Journal of Fish Biology, 74 (4): 961-966.

Arme, C., P. Pappas. 1983. Biology of the Eucestoda. New York, New York: Academic Press Inc.

Ekbaum, E. 1935. Notes on the species of Triaenophorus in Canada. The American Society of Parasitologists, 21 (4): 260-263. Accessed March 23, 2011 at

Lahnstein, F., M. Kletzl, T. Weismann. 2009. The risk of parasite transfer to juvenile fishes by live copepod food with the example of Triaenophorus crassus and Triaenophorus nodulosus. Aquaculture, 295 (1-2): 120-125.

Miller, R.B., 1952. A review of the Triaenophorus problem in Canadian lakes. Bulletin of the Fisheries Research Board of Canada, 95: 1-42.

Ondrackova, D., M. Pecinkova, R. Blazek, M. Gelnar, Z. Valova. 2005. Metazoan parasites of Neogobius fishes in the Slovak section of the River Danube. Journal of Applied Ichthyology, 21 (4): 345-349.

Ondrackova, M., T. Trichkova, P. Jurajda. 2006. Present and historical occurrence of metazoan parasites in Neogobius kessleri ( Pisces:Gobiidae) in the Bulgarian section of the Danube River. Acta Zoologica Bulgaria, 58 (3): 401-408.

Pulkkinen, K., E. Valtonen, A. Niemi, K. Poikola. 1999. The influence of food competition and host specifity on the transmission of Triarnophorus crassus (Cestoda) and Cystidicola farionis (Nematoda) to Coregonus lavaretus and Coregenus albula (Pisces:Coregonidae) in Finland. International Journal of Parasitology, 29: 1754-1763.

Pulkkinen, K., A. Pasternak, T. Hasu, E. Valtonen. 2000. Effect of Triaenophorus crassus (Cestoda) infection on behavior and susceptibilty to predation of the first intermediate host Cyclops strennus. The American Society of Parasitologists, 86 (4): 664-670.

Rahkonen, R., P. Koski. 1997. Occurrence of cestode larvae in brown trout after stocking in a large regulated lake in northern Finland. Diseases of Aquatic Organisms, 31 (1): 55-63.

Southwell, T. 1930. The Fauna of Brithish India, Cestoda. London: Taylor and Francis.

Uzmann, J., M. Hesselholt. 1957. New host and locality record for Triaenophorus crassus Florel (Cestoda: Pseudophyllidea). The American Society of Parasitologists, 43 (2): 205-208.

Vickova, R., L. Poddubnaya, R. Kuchta, A. Gustinell, E. Dzika. 2007. Invalidity of the three Palaearctic species of Triaenophorus tapeworms (Cestoda: Pseudophyllidea): evidence from morphometric analysis of the scolex hooks. Faculty of Biological Sciences, 54 (1): 34-42.

Wardle, R., J. McLeod, S. Radinovsky. 1974. Advances in the Zoology of Tapeworms 1950-1970. United Kingdom and India: Oxford University Press, London and Delhi.