The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Schyzocotyle acheilognathi
Schyzocotyle acheilognathi
(Asian tapeworm)

Copyright Info
Schyzocotyle acheilognathi (Yamaguti, 1934)

Common name: Asian tapeworm

Synonyms and Other Names: Bothriocephalus aegyptiacus, Bothriocephalus gowkongensis, Bothriocephalus kivuensis, Bothriocephalus opsariichthydis, Bothriocephalus phoxini, Schyzocotyle fluviatilis, Schyzocotyle acheilognathi

Taxonomy: available through www.itis.govITIS logo

Identification: Schyzocotyle acheilognathi is a cestode which parasitizes freshwater fish, particularly cyprinids (Marcogliese, 2008).  It can be identified by a unique fleshy, arrow-head or heart shaped scolex (head region) with a relatively undeveloped terminal disc, and two anterolaterally directed bothria (slit-like openings) which are short and deep (Scholz, 1997).  It has no neck; instead, proglottids (body segments) begin directly behind the scolex.  The proglottids are relatively elongate and much narrower than the scolex (Scholz, 1997).  

Native Range: Native to East Asia and China, Schyzocotyle acheilognathi was first described by S. Yamaguti in 1934 from Ogura Lake, Japan (Scholz, 1997).

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Schyzocotyle acheilognathi are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
AZ197919995Grand Canyon; Kanab; Lower Colorado-Marble Canyon; Lower Little Colorado; Lower Virgin
CA200120017Aliso-San Onofre; Los Angeles; Salton Sea; San Jacinto; Santa Ana; Santa Clara; Santa Margarita
CO200420041Lower Yampa
HI199319953Hawaii; Kauai; Oahu
MI200120022Detroit; Ontonagon
NV197919932Lower Virgin; Muddy
NM200720072Upper Pecos; Upper Pecos-Long Arroyo
NY201820181Upper Susquehanna
NC198719871Upper Dan
TX199920076Big Bend; Cibolo-Red Light; Elm-Sycamore; International Falcon Reservoir; Lower Devils; San Ambrosia-Santa Isabel
UT198519851Upper Virgin
WI200120011Upper Wisconsin

Table last updated 6/18/2024

† Populations may not be currently present.

Ecology: Schyzocotyle acheilognathi has a less complex life cycle than many tapeworm species, requiring only one intermediate host before reaching its final host (Hansen et. al, 2007). The adult worm is an intestinal parasite in fish. It absorbs nutrients directly across the tegument (body covering), competing with the host animal for nutrition (Hansen et al. 2006). 
Adult worms are hermaphroditic; each proglottid has a complete set of both male and female reproductive organs and produces eggs through self-fertilization.  The eggs are shed into the water with the host's fecal material, where they hatch into free-swimming hexacanth (six-hooked) larvae.  Eggs require water temperatures between 12ºC and 37ºC to hatch.  Within this range, the amount of time required for hatching varies with water temperature.  Eggs tend to hatch within 1-5 days at 28-30ºC, and within 10-28 days at 14-15ºC (Marcogliese, 2008).
The free-swimming larvae, called coracidia, are consumed by cyclopoid copepods (tiny crustaceans).  They then burrow into the copepod's haemocoel (body cavity), where they develop into a second larval stage called a procercoid.  This process also depends upon water temperature; larvae become able to infect their final host in 11-18 days at 29-31ºC, and in 49 days at 20ºC (Marcogliese, 2008). Schyzocotyle acheilognathi is a true generalist, infecting a wide vareity of hosts, which contributes to its invasiveness (Choudhury and Cole 2012, Scholz et al. 2012).
While fish are normally infected by consuming infected copepods, there is some evidence that adult worms can be transmitted directly to piscivorous fish that prey on infected fish (Hansen et al., 2007).  Once within the host fish's intestine, the larvae mature into adult worms over the course of 21-23 days at 28-29ºC (Marcogliese, 2008).

Common Carp (Cyprinus carpio) and Grass Carp (Ctenopharyngodon idella) are the principle native hosts for the Asian tapeworm, but it has an extremely low degree of host specificity, and has been found in fish species from 12 families and 6 orders worldwide (Dove and Fletcher, 2000). In a review of 651 studies, Kuchta et al. (2018) found that S. acheilognathi can infect 312 fish species from 38 families and 14 orders, with species from the family Cyprinidae being the most commonly infected. Futhermore, the same study found that 11 non-fish species (5 amphibians, 1 reptile, 4 birds, and 1 mammal [humans]) can be infected although these non-fish are not thought to be definitive hosts. However, non-fish hosts, particularly aquatic birds, may be able to act as vectors transporting this parasite among water bodies (Kuchta et al. 2018).


Means of Introduction: Schyzocotyle acheilognathi was first identified in North America in 1975 in Golden Shiner (Notemigonous crysoleucas) and Fathead Minnow (Pimephales promelas)(Kuchta et al. 2018). It is likely to have been accidentally introduced into North America as early as 1963 with Grass Carp (Ctenopharyngodon idella), one of its native hosts, and subsequently spread through the translocation of bait fish (Choudhury et al. 2006; Heckmann et al. 1993; Kuchta et al. 2018). For example, Heckmann et al. (1993) found infected minnows in four bait shops near Las Vegas, NV, that had originated from commercial ponds outside the state and Boonthai et al. (2017) found S. acheilognathi to be widespread in baitfish in Michigan. 

Status: This parasite has become widespread, and is known in several areas of the United States. It appears to be well established in the lower Colorado River and the Hawaiian islands (Choudhury et al., 2006), and has been reported in the Great Lakes (Marcogliese, 2008) and Susquehanna River watershed (Reyda et al. 2019). 

Impact of Introduction: Infection with Schyzocotyle acheilognathi acheilognathi has been shown to reduce a fish's ability to cope with stressors such as reduced food availability (Hansen, et al., 2006).  Competing with intestinal parasites for nutrients may lead to reduced body condition, anemia, reduced growth and  temperature-dependent mortality, especially in juvenile fish. Other known pathogenic effects include intestinal inflammation,  protein depletion and altered digestive enzyme activity (Marcogliese, 2008). Infected baitfish in Michigan exhibited symptoms including enlargement of the abdomen, intestinal distension, and intestinal occlusion and hemorrhage (Boonthain et al. 2017).

S. acheilognathi is known to infect wild populations of the federally endangered Humpback Chub (Gila cypha), Mojave Tui Chub (Siphateles bicolor mohavensis), Virgin Roundtail Chub (Gila robusta seminuda), and Woundfin Minnow (Plagopterus argentissimus), as well as several other rare and/or endemic fishes in the western United States, including Virgin Spinedace (Lepidomeda mollispinis mollispinis), Roundtail Chub (Gila robusta), Arroyo Chub (Gila orcutta), and Tamaulipas Shiner (Notropis braytoni) (Bean et al., 2007; Clarkson et al. 1997; Heckmann et al., 1986; Warburton et al., 2002; Ward, 2005). The federally endangered bonytail chub (Gila elegans) has also been shown experimentally to be a suitable host (Hansen et al., 2006). The increased stress of tapeworm infection may severely complicate efforts at conservation and recovery for these species.  In Hawaii, at least two of the five native freshwater fish species have been found to be infected (Font and Tate, 1994).  This is concerning because geographic isolation makes Hawaiian species inherently vulnerable. 

References: (click for full references)

Alexander, J. 2008. New tapeworm found in Great Lakes fish. LaCrosse Fish Health Center. http://www.fws.gov/midwest/LaCrosseFishHealthCenter/Documents/MskegonAsianTW.pdf. Accessed 19 June 2012.

Bean, M. G.  2008.  Occurrence and impact of the Asian fish tapeworm Bothriocephalus acheilognathi in the Rio Grande (Rio Bravo del Norte).  MS Thesis. Texas State University, San Marcos.

Bean, M. G., A. Skerikova, T. H. Bonner, T. Scholz, and D. G. Huffman. 2007.  First record of Bothriocephalus acheilognathi in the Rio Grande with comparative analysis of ITS2 and V4-18S rRNA gene sequences.  Journal of Aquatic Animal Health 19: 71-76.

Boonthai, T., S.J. Herbst, G.E. Whelan, M.G. Van Deuren, T.P. Loch, and M. Faisal. 2017. The Asian fish tapeworm Schyzocotyle acheilognathi is widespread in baitfish retail stores in Michigan, USA. Parasites and Vectors 10(618):1-10.

Brandt, F.W., J.G. Van As, H.J. Schoombee, and V.L. Hamilton-Attwell. 1981. The occurrence and treatment of bothriocephalosis in the common carp, Cyprinus carpio in fish ponds with notes on its presence in the largemouth yellowfish Barbus kimberleyensis from the Vaal Dam, Transvaal. Water SA 7:35-42.

Brouder, M. J., and T. L. Hoffnagle. 1997.  Distribution and prevalence of the Asian fish tapeworm, Bothriocephalus acheilognathi, in the Colorado River and tributaries, Grand Canyon, Arizona, including two new host records.  Journal of the Helminthological Society of Washington 64(2): 219-226.

Brouder, M. 1999. Relationship between length of roundtail chub and infection intensity of Asian fish tapeworm Bothriocephalus acheilognathi. Journal of Aquatic Animal Health 11(3):302-304.

Carpenter, S.R., J.J. Cole, J.R. Hodgson, J.F. Kitchell, M.L. Pace, D. Bade, K.L. Cottingham, T.E. Essington, J.N. Houser, and D.E. Schindler. 2001. Trophic cascades, nutrient, and lake productivity: Experimental enrichment of lakes with contrasting food webs. Ecological Monographs 71:163-186.

Choudhury, A., T.L. Hoffnagle, and R.A. Cole. 2004. Parasites of native and nonnative fishes in the Little Colorado River, Grand Canyon, Arizona. Journal of Parasitology 90:1042-1052.

Choudhury, A., E. Charipar, P. Nelson, J. R. Hodgson, S. Bonar, and R. A. Cole.  2006. Update on the distribution of the invasive Asian fish tapeworm, Bothriocephalus acheilognathi, in the U.S. and Canada.  Comparative Parasitology 73(2): 269-273.

Choudury, A., R. Cole. 2012. Bothriocephalus acheilognathi Yamaguti (Asian tapeworm). Pages 389-404 in Francis, R.A. (Ed.), A Handbook of Global Freshwater Invasive Species. Earthscan, London.

Clarkson, R. W., A. T. Robinson, and T. L. Hoffnagle. 1997. Asian tapeworm (Bothriocephalus acheilognathi) in native fishes from the Little Colorado River, Grand Canyon, Arizona.  Great Basin Naturalist 57(1): 66-69.

Dove, A. D. M., and A. S. Fletcher. 2000.  The distribution of the introduced tapeworm Bothriocephalus acheilognathi in Australian freshwater fishes.  Journal of Helminthology 74: 121-127.

Font, W. F., and D. C. Tate. 1994. Helminth parasites of native Hawaiian freshwater fishes: an example of extreme ecological isolation.  Journal of Parasitology 80(5): 682-688.

Hansen, S. P., A. Choudhury, and R. A. Cole. 2007. Evidence of experimental postcyclic transmission of Bothriocephalus acheilognathi in bonytail chub (Gila elegans). Journal of Parasitology 93(1): 202-204.

Hansen, S. P., A. Choudury, D. M. Heisey, J. A. Ahumada, T. L. Hoffnagle, and R. A. Cole. 2006. Experimental infection of the endangered bonytail chub (Gila elegens) with the Asian fish tapeworm (Bothriocephalus acheilognathi): impacts on survival, growth and condition. Canadian Journal of Zoology 84: 1383-1394.

Heckmann, R. A., and J. E. Deacon. 1987.  New host records for the Asian fish tapeworm, Bothriocephalus acheilognathi, in endangered fish species from the Virgin River, Utah, Nevada, and Arizona.  Journal of Parasitology 73(1): 226-227.

Heckmann, R. A., J. E. Deacon, and P. D. Greger. 1986. Parasites of the woundfin minnow, Plagopterus argentissimus, and other endemic fishes from the Virgin River, Utah.  Great Basin Naturalist 46(4): 662-676.

Heckmann, R. A., P. D. Greger, and R. C. Furtek. 1993. The Asian fish tapeworm, Bothriocephalus acheilognathi, in fishes from Nevada.  Journal of the Helminthological Society of Washington 60(1): 127-128.

Korting, W. 1974. Bothriocephalosis of the carp. Veterinar-Medizinische Nachrichten 2(74):152-158.

Kuchta, R., A. Choudhury, T. Scholz. 2018. Asian fish tapeworm: the most successful invasive parasite in freshwaters. Trends in Parasitology 34(6):511-523.

Lafferty, K.D., and A.K. Morris. 1996. Altered behavior of parasitized killifish increases susceptibility to predation by bird final hosts. Ecology 77(5):1390-1397.

Maldonado, G.S., and R.F. Lopez. 2003. The Asian fish tapeworm Bothriocephalus acheilognathi: a potential threat to native freshwater fish species in Mexico. Biological Invasions 5:261-268.

Marcogliese, D. J.  2008. First report of the Asian fish tapeworm in the Great Lakes.  Journal of Great Lakes Research 34: 566-569.

Mitchell, A., and A. Darwish. 2009. Efficacy of 6-, 12-, and 24-h praziquantel bath treatments against Asian tapeworms Bothriocephalus acheilognathi in grass carp. North American Journal of Aquaculture 71:30-34.

Mitchell, A.J., and G.L. Hoffman. 1980. Important tapeworms of North American freshwater fishes. US Department of Interior Fish & Wildlife Service. Fish Disease Leaflet 59, 17 pp.

New York State Department of Environmental Conservation (NYDEC). 2012. Redfin Shiner Fact Sheet. http://www.dec.ny.gov/animals/26014.html. Accessed 21 June 2012.

Ohio Department of Natural Resources (ODNR). 2012. Golden shiner. http://www.dnr.state.oh.us/Home/species_a_to_z/SpeciesGuideIndex/goldenshiner/tabid/6640/Default.aspx. Accessed 21 June 2012.

Paperna, I. 1996. Parasites, infections and diseases of fishes in Africa, An update. Food and Agriculture Organization of the United Nations. CIFA Technical Paper, 31. 204 pp.

Pool, D. W. 1987. A note on the synonomy of Bothriocephalus acheilognathi Yamaguti, 1934, B. aegyptiacus Rysavy and Moravec, 1975 and B. kivuensis Baer and Fain, 1958.  Parasitology Research 73: 146-150.

Reyda, F.B., C.P. Pommelle, and M.L. Doolin. 2019. Asian Fish Tapeworm (Schyzocotyle acheilognathi) found in New York State for the first time after a long-term fish-parasite survey. Comparative Parasitology 86(2):108-113. 

Riggs, M. R., and G. W. Esch. 1987. The suprapopulation dynamics of Bothriocephalus acheilognathi in a North Carolina reservoir; abundance, dispersion, and prevalence.  Journal of Parasitology 73(5): 877-892.

Scholz, T.  1997.  A revision of the species of Bothriocephalus Rudolphi, 1808 (Cestoda: Pseudophyllidea) parasitic in American freshwater fishes. Systematic Parasitology 36: 85-107.

Scholz, T., R. Kuchta, C. Williams. 2012. Bothriocephalus acheilognathi. Pages 282-297 in Woo, P.T.K., K. Buchmann (Eds.), Fish Parasites: Pathobiology and Protection. CAB International, Wallingford.

U.S. Fish & Wildlife Service (USFWS). 2012. National Wild Fish Health Surveys. http://www.fws.gov/wildfishsurvey/regionalpath.htm. Accessed 19 June 2012.

Vincent, A. G., and W. F. Font. 2003. Host specificity and population structure of two exotic helminths, Camallanus cotti (Nematoda) and Bothriocephalus acheilognathi (Cestoda), parasitizing exotic fishes in Waianu Stream, O'ahu, Hawai'i.  Journal of Parasitology 89(3): 540-544.

Warburton, M., B. Kuperman, V. Matey, and R. Fisher.  2002. Parasite analysis of native and non-native fish in the Angeles National Forest.  Final Report, U.S. Geological Survey Western Ecological Research Center, San Diego, CA.

Ward, D. 2005.  Collection of Asian tapeworm (Bothriocephalus acheilognathi) from the Yampa river, Colorado.  Western North American Naturalist 65(3): 403-404.

Other Resources:
Great Lakes Waterlife

Author: Hejna, M. A.K. Bogdanoff, A. Fusaro, S. Iott and R. Sturtevant

Revision Date: 9/13/2019

Citation Information:
Hejna, M. A.K. Bogdanoff, A. Fusaro, S. Iott and R. Sturtevant, 2024, Schyzocotyle acheilognathi (Yamaguti, 1934): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=2798, Revision Date: 9/13/2019, Access Date: 6/18/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [6/18/2024].

Contact us if you are using data from this site for a publication to make sure the data are being used appropriately and for potential co-authorship if warranted.

For general information and questions about the database, contact Wesley Daniel. For problems and technical issues, contact Matthew Neilson.