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

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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).

Great Lakes Nonindigenous Occurrences: Schyzocotyle acheilognathi has been introduced in Europe, Australia, Mexico, the United States, and Puerto Rico (Marogliese, 2008). It has also been reported in Manitoba, Canada (Choudhury et al. 2006). This species is now found on every continent on the planet with the exception of Antartica (Choudhury and Cole 2012, Schloz et al. 2012).

The first collection of this species in the Great Lakes region was two gravid S. acheilognathi collected from a Fathead Minnow (Pimephales promelas) in Peter Lake, Michigan in 2001 (Choudhury et al. 2006). In 2004, a single mature S. acheilognathi was collected from a Bluntnose Minnow (Pimephales notatus) in Grosse Isle, Michigan (Marcogliese 2008). The parasite is believed to have been introduced to Land o’ Lakes, Wisconsin with infected Golden Shiner during a food-web manipulation study (Choudhury et al. 2006).  Many additional reports of this genus throughout the Great Lakes region have not been identified to species making it difficult to ascertain the true distribution of this species.

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, 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.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
MI200120022Detroit; Ontonagon

Table last updated 12/2/2023

† 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). 

Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...



There is little or no evidence to support that Schyzocotyle acheilognathi has significant environmental impacts in the Great Lakes.
Historically, S. acheilognathi has had a limited distribution in the Great Lakes infecting several native species including Fathead Minnow (Pimephales promelas), Bluntnose Minnow (P. notatus), and Golden Shiner (Notropis crysoleucas) (Choudhury et al. 2006, Marcogliese 2008).

Common Carp (Cyprinus carpio) and Grass Carp (Ctenopharyngodon idella) are principle hosts for Asian tapeworm. However, S. acheilognathi displays a low degree of host specificity (Dove and Fletcher 2000, Maldonado 2003). In 2003, an immature specimen of S. acheilognathi was collected from a White Bass (Morone chrysops) in Lake Winnipeg, Manitoba, Canada (Choudhury et al. 2006).

The Great Lakes native Redfin Shiner (N. umbratilus) has been found harboring this parasite in parts of Nebraska (Choudhury et al. 2006); however, no infections of Asian tapeworm in Redfin Shiner have been realized in the Great Lakes. Redfin Shiner is considered a species of special concern in New York (NYDEC 2012).

Schyzocotyle acheilognathi infects other U.S. species of importance including Roundtail Chub (Gila robusta) (Brouder 1999), the endangered Bonytail Chub (G. elegans) (Hansen et al. 2006), and the endangered Humpback Chub (G. cypha) (Choudhury et al. 2004, Hansen et al. 2006) and is listed as a “Pathogen of Regional Importance” in the southwestern U.S. (USFWS 2012).

Parasitic nutrient competition may lead to reduced body condition and growth, anemia, and temperature-dependent mortality in infected host fish. Pathogenic effects include intestinal inflammation, protein depletion, and altered digestive enzyme activity (Marcogliese 2008). Because of this, infected fish are more susceptible to predation (Lafferty and Morris 1996). However, cascading food web effects have not been reported as a result of S. acheilognathi infection in the Great Lakes.

There is little or no evidence to support that Schyzocotyle acheilognathi has significant socio-economic impacts in the Great Lakes.
Tapeworm-parasitized fish are safe to consume, provided the fish are thoroughly cooked, smoked, or pickled (Alexander 2008).

Golden Shiner and Fathead Minnow are the most common commercially farmed baitfish in the United States (ODNR 2012).

There is little or no evidence to support that Schyzocotyle acheilognathi has significant beneficial effects in the Great Lakes.
Common Carp (Cyprinus carpio) and Grass Carp (Ctenopharyngodon idella) are principal hosts for Asian tapeworm (Dove and Fletcher 2000), infection of which could lead to population reductions in those non-native species.


Regulations (pertaining to the Great Lakes)
There are no known regulations for this species.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

There are no known biological control methods for this species.

There are no known physical control methods for this species.

Bath treatments are effective control methods for S. acheilognathi infections. Baths should contain Droncit® (praziquantel), isopropyl alcohol, and water yielding a final mixture concentration ≥ 0.67 ppm praziquantel. Fish densities during treatment should be no greater than 60 mg fish/L and exposure should last 24 hours. After 24 hours, the treatment should be drained, worm parts discarded, and clean water added. After 72 hours, the treatment should be drained and worm parts discarded. Fish should then be transferred to a decontaminated container (Mitchell and Darwish 2009).

Schyzocotyle acheilognathi infections can be treated with chemically enhanced feed. Drugs should be mixed in oil and sprayed on feed at a rate of 1 L/70 kg dry weight. Effective chemicals and doses include dibutylin oxide or dibutylin dilurate (250 mg/kg fish) fed over 3 days (Mitchell and Hoffman 1980), Yomesan® (500 g/500 kg dry pellets) fed at 1.5% of body weight 2–3 times weekly, and Yomesan® (28 g/40 kg) fed for 3 days (Brandt et al. 1981, Korting 1974, Mitchell and Hoffman 1980).

Schyzocotyle acheilognathi populations in aquaculture and ponds can be controlled by managing the intermediate host (i.e., copepods) population densities. Effective ectoparasiticides include Neguvon®, Masoten®, Dipterex®, Bromex®, and Naled® (Paperna 1996).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

References (click for full reference list)

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

Contributing Agencies:

Revision Date: 9/13/2019

Citation for this information:
Hejna, M. A.K. Bogdanoff, A. Fusaro, S. Iott and R. Sturtevant, 2023, Schyzocotyle acheilognathi (Yamaguti, 1934): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 9/13/2019, Access Date: 12/2/2023

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.