Bothriocephalus aegyptiacus Rysavy et Moravec, 1975, Bothriocephalus gowkongensis Yeh, 1955, Bothriocephalus kivuensis Baer et Fain, 1958, Bothriocephalus opsariichthydis Yamaguti, 1934, Bothriocephalus phoxini Molnar, 1966, Schyzocotyle fluviatilis Akhmerov, 1960

Schyzocotyle acheilognathi is a true generalist, infecting a wide variety of host species (but primarily fish), which contributes to its invasiveness (Choudhury and Cole 2012, Scholz et al. 2012). Common Carp (Cyprinus carpio) and Grass Carp (Ctenopharyngodon idella) are the principal native hosts for the Asian tapeworm, and Bighead carp (Hypophthalmichthys nobilis) are also noted as occasional hosts, but it has an extremely low degree of host specificity (Dove and Fletcher 2000, Chakraborty 2024), meaning that it can infect multiple species. 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. 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, aquatic birds may be able to transport this parasite among water bodies (Kuchta et al. 2018).

Food Web:

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).

Life History:
Schyzocotyle acheilognathi has a less complex life cycle than many tapeworm species, requiring only one intermediate host (a copepod) before reaching its final host (Hansen et. al, 2007).    

Adult worms are hermaphroditic; each proglottid has a complete set of both male and female reproductive organs and can produce eggs through self-fertilization as well as with two parents. Egg release first occurs 130-200 days after infection and then continues constantly; the number of eggs per adult worm varies significantly but may exceed 5000/day and 180,000 over its lifetime (Pool 1985).   Eggs require water temperatures between 12ºC and 37ºC to hatch but can be frozen for up to 72 hours without significant mortality, and can be held at 4ºC for >60days and still hatch when returned to warmer temperatures.  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).  Thermal optima for hatching is 30ºC, which is warmer than most fish tapeworms.

The eggs are shed into the water with the host's fecal material, where they hatch into free-swimming hexacanth (six-hooked) larvae. The lifespan of the free-living larvae is limited (typically less than 48 hours) and dependent on temperature and internal energy reserves; at higher temperatures, internal energy reserves are exhausted more quickly (Pool 1985, Falcón-Ordaz and García-Prieto 2008). The larvae 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 (range 10-30ºC); larvae become able to infect their final host in 11-18 days at 29-31ºC, and in 49 days at 20ºC (Pool 1985, Marcogliese 2008). 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). Longevity of adult worms is INVERSELY related to temperature, at 30ºC they survive ~100 days and at 18ºC up to 670 days.  This allows adult worms to overwinter (Pool 1985). 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).

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

Environmental	Socioeconomic	Beneficial

Historically, S. acheilognathi has had a limited geographic distribution in the Great Lakes (Huron-Erie corridor) 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 principal hosts for Asian tapeworm. However, S. acheilognathi displays a low degree of host specificity (Dove and Fletcher 2000, Maldonado 2003) and this parasite has been identified in many Great Lakes fish species (Choudhury et al. 2006, Reyda et al 2019). Outside the Great Lakes, 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.

Golden Shiner and Fathead Minnow, which are susceptible to this parasite, 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)
 

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

Control
PCR and LAMP assays are available to support early detection (Hofmeister et al. 2021).

Chemical
Bath treatments are effective control methods for S. acheilognathi infections. Baths should contain 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) and niclosamide(Brandt et al. 1981, Korting 1974, Mitchell and Hoffman 1980).

Other
Schyzocotyle acheilognathi populations in aquaculture and ponds can be controlled by managing the intermediate host (i.e., copepods) population densities (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.