Craspedacusta sowerbyi Lankester, 1880

Common Name: Freshwater jellyfish

Synonyms and Other Names:

peach blossom fish (China); Craspedacusta sowerbii (Lankester, 1880)

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Identification: Craspedacusta sowerbyi is a hydrozoan (Phylum Cnidaria, Class Hydrozoa), which is most easily identified when it takes the form of a small, bell-shaped jellyfish, known as a hydromedusa.  The hydromedusa measures about 5–25 mm in diameter, and is translucent with a whitish or greenish tinge (Peard, 2002; Pennak, 1989).  It possesses five opaque-white canals, which form the gastrovascular cavity; four are radial and one is medially dorsoventral.  Tentacles of varying lengths protrude from the upper margin of the velum, arranged with three to seven short tentacles between longer ones (Pennak, 1989; Slobodkin and Bossert, 1991).  Freshwater jellyfish exhibit four very long tentacles, each parallel to a radial canal at the edge of the velum.  Shorter tentacles facilitate feeding, while the longer ones give stability for swimming.  The total number of tentacles varies from 50 to 500 (Pennak, 1989).  Conspicuous swarms of hydromedusae appear sporadically, but are only one part of the animal's life cycle.  Craspedacusta sowerbyi more often exist as microscopic podocysts (dormant "resting bodies"), frustules (larvae produced asexually by budding), planulae (larvae produced sexually by the hydromedusae), or as sessile polyps, which attach to stable surfaces and can form colonies consisting of two to four individuals and measuring 5 to 8 mm (Angradi, 1998; Acker and Muscat, 1976; Pennak, 1989; Peard, 2002).

Size: hydromedusa is 5–25 mm in diameter

Native Range: Craspedacusta sowerbyi is indigenous to the Yangtze River valley in China, where it can be found in both the upper and lower river valley (Slobodkin and Bossert, 1991). 

Great Lakes Nonindigenous Occurrences: Craspedacusta sowerbyi was discovered in the Huron River near Ann Arbor, MI, in 1933, and in Lake Erie shortly thereafter (Mills et al., 1993).  It has since been recorded in Lake Huron and Lake St. Clair, as well as dozens of inland lakes and streams throughout the region, in the states of IL, IN, MI, MN, NY, OH, PA, and WI.  In Canada, freshwater jellyfish have been known in Quebec since 1955 and in Ontario since 1980 (Peard, 2002).

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 Craspedacusta sowerbyi are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IN199920153Little Calumet-Galien; St. Joseph; St. Joseph
MI1933202326Au Sable; Betsie-Platte; Black; Black-Macatawa; Boardman-Charlevoix; Brule; Cheboygan; Clinton; Flint; Huron; Kalamazoo; Lake Huron; Lake St. Clair; Lone Lake-Ocqueoc; Lower Grand; Manistee; Muskegon; Ontonagon; Pere Marquette-White; Pine; Raisin; St. Clair; St. Joseph; Thornapple; Tittabawassee; Upper Grand
MN200320202Cloquet; St. Louis
NY1934202213Ausable River; Black; Grass; Lake Champlain; Lake Erie; Oneida; Oswegatchie; Raisin River-St. Lawrence River; Raquette; Salmon-Sandy; Saranac River; Seneca; St. Regis
OH193320058Auglaize; Black-Rocky; Cedar-Portage; Cuyahoga; Grand; Lake Erie; Lower Maumee; Sandusky
VT199920185Mettawee River; Missiquoi River; Otter Creek; St. Francois River; Winooski River
WI199820168Bad-Montreal; Beartrap-Nemadji; Black-Presque Isle; Lake Michigan; Menominee; Oconto; Upper Fox; Wolf

Table last updated 12/1/2023

† Populations may not be currently present.

Ecology: Craspedacusta sowerbyi occupies a range of freshwater habitats.  In its native range, it typically inhabits shallow pools along the Yangtze River, sometimes coexisting with a related species, C. sinensis, which occurs in the upper river valley (Slobodkin and Bossert, 1991).  In this environment, changing conditions in the main river system expose jellyfish to fluctuating water levels, temperatures and plankton populations. Where it is introduced, C. sowerbyi is most commonly found in shallow, slow moving or stagnant artificial water bodies such as ornamental ponds, reservoirs, gravel pits, and quarries (Pennak, 1956; DeVries, 1992; Peard, 2002). They prefer still or slow moving freshwater bodies of mesotrophic character between 12 and 33 degrees Celsius (Galarce et al., 2013).  It has also been reported in large river systems, including the Allegheny, Ohio and Tennessee River systems, natural lakes, aquaria, and ornamental ponds (Beckett and Turanchik, 1980; DeVries, 1992; Peard, 2002). A study by Caputo et al. 2018, demonstrated that higher turbidity or increase in color of the water ‘‘brownification’’ would provide more favorable conditions for the invasion process of this hydroid.
    Craspedacusta sowerbyi is able to reproduce both sexually and asexually.  Mature hydromedusae reproduce sexually by broadcasting gametes into the water.  Fertilized eggs grow into ciliated planulae (larvae), which then settle and metamorphose into the polyp form.  Polyps are capable of budding to produce hydromedusae, as well as either daughter polyps that remain attached to the parent, forming a colony, or frustule larvae which move to new locations before metamorphosing into new polyps (Pennak, 1989; Slobodkin and Bossert, 1991; Peard, 2002).
    Hydromedusae are produced only sporadically, and a given location may go several years between blooms (Peard, 2002).  Blooms are thought to be temperature dependent, requiring water of at least 25° C, and are most common in summer and fall (Kato and Hirabayashi, 1991; Dodson and Cooper, 1983; Anonymous, 1997; McGaffin, 1997; Peard, 2002).  Other factors that may affect hydromedusa blooms include zooplankton populations, alkalinity, and calcium carbonate (Acker and Muscat, 1976; Koryak and Clancy, 1981; McCullough et al., 1981; Angradi, 1998). The more cold tolerant polyp form may have a wider distribution than the hydromedusa form, but because it is inconspicuous and easily overlooked, its range is difficult to determine (Kato and Hirabayashi, 1991; Angradi, 1998).  Polyps overwinter by contracting into resting bodies called podocysts, which are essentially dormant cellular balls surrounded by a protective chitin-like membrane that allows them to withstand more extreme conditions than the active forms (Peard, 2002).  When conditions are favorable, the podocysts grow into polyps again.
    Like other cnidarians, C. sowerbyi is an opportunistic predator, feeding on small organisms that come within its reach. A study in Northern Italy found that C. sowerbyi feed on zooplankton with a preference for the Daphnia complex of species (Stefani et al., 2010). Both polyp and hydromedusa forms use nematocysts (stingers) to capture prey.  Polyps are able to camouflage themselves by secreting a sticky mucous that adheres particles to their body (Pennak, 1989; Peard, 2002).

Means of Introduction: Initially, C. sowerbyi was probably transported with ornamental aquatic plants, especially water hyacinth (Eichhornia crassipes), from its native region in China (Slobodkin and Bossert, 1991). An introduction at Fena Lake, Guam may have accompanied the introduction of tilapia following dam construction in 1952.  The first sightings of C. sowerbyi at Fena Lake were in 1970 (Belk and Hotaling, 1971).  In the United States, polyps and resting bodies are probably translocated accidentally with stocked fish and aquatic plants or by waterfowl  (Angradi, 1998; Wynett and Wynett, pers. comm. 1998).  Pennak (1956) noted that new reservoirs and ponds (less than 40 years) exhibited the majority of hydromedusa blooms known at that time.

Status: Craspedacusta sowerbyi is apparently established throughout most of the United States.  Since the first record in 1880, it has been recorded in 44 states and the District of Columbia (Pennak, 1989; DeVries, 1992; Peard, 2002).   In Colorado, only two populations have been reported, so the species may not be established there (Pennak, 1956; DeVries, 1992; Peard, 2009). The presence of C. sowerbyi in Maui, Hawaii was confirmed in 1938, however its status in Hawaii is unknown.  There have been no documented observations of C. sowerbyi in Hawaii for at least 15 years (Edmondson, 1940; Eldredge, personal communication 2002). 

Great Lakes Impacts: Current research on the environmental impact of Craspedacusta sowerbyi in the Great Lakes is inadequate to support proper assessment.

The impact of this widespread hydroid is unclear. Many studies of Craspedacusta sowerbyi feeding behavior have concluded that this species could have significant impacts on zooplankton communities due to increased predation pressure and prey preference (e.g., Smith and Alexander 2008, Stefani et al. 2010). For instance, Dodson and Cooper (1983) proposed that C. sowerbyi's preference for predatory zooplankton, such as the rotifer Asplanchna, could influence relative zooplankton species structure. Spadinger and Maier (1999) agreed with theorized effects on zooplankton communities, finding that C. sowerbyi hydromedusae prefer larger zooplankton (0.4–1.4 mm) and vigorous prey such as copepods. In a study of how C. sowerbyi predation could affect the traits of prey species, Jankowski (2004) found that C. sowerbyi predation did not appear to have a significant effect on the life history or development of Bosmina longirostris. However, predation pressure did appear to induce some morphological changes, such as increased lengths of both mucro and antennae as a defense mechanism (Jankowski 2004).

A European study used field enclosures and microcosms to test the potential effects of C. sowerbyi presence on the local ecosystem and found that there was a significant decrease in small crustaceans (especially juvenile cyclopoid copepods and B. longirostris) in microcosms with C. sowerbyi and a significant increase in chlorophyll concentration in enclosures with C. sowerbyi (Jankowski et al. 2005). The latter of these observations indicates that C. sowerbyi may be capable of contributing to trophic cascade effects. However, in situ evidence of C. sowerbyi impacts on the zooplankton community or other trophic levels is currently lacking.

Direct and indirect impacts of C. sowerbyi on fish populations are also unclear. Under laboratory conditions and in 4 mm of water, C. sowerbyi polyps have killed and fed on striped bass larvae (Dendy 1978). Dumont (1994) speculated that C. sowerbyi may consume fish eggs, but Spadinger and Maier (1999) note that it is generally not considered an important predator of eggs or small fish. Crayfish are considered the only important predator of the hydromedusa phase (Pennak 1989, Slobodkin and Bossert 1991). Because C. sowerbyi populations are not checked by predation, freshwater jellyfish may be and have been abundant in ecosystems where fish abundance is also high, despite the potential for competition over food resources (Jankowski et al. 2005). Adverse effects on fish populations due to C. sowerbyi-related food web alterations have yet to be documented.

There is little or no evidence to support that Craspedacusta sowerbyi has significant socio-economic impacts in the Great Lakes.

There is little or no evidence to support that Craspedacusta sowerbyi has significant beneficial effects in the Great Lakes.

Management: 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.

Craspedacusta sowerbyi has spread across temperate climates for more than a century, but despite experimental observation of its possible contribution to trophic cascade effects (Jankowski et al. 2005), and studies on predation habits (Dodson and Cooper 1983, Spadinger and Maier 1999, Dendy 1978), little research on control is available.

There are no known biological control methods for this species. Craspedacusta sowerbyi populations are not checked by predation (Jankowski et al. 2005).

There are no known physical control methods for this species. Hydrozoan hydromedusae blooms are known to be temperature dependent (Ma and Purcell 2005), but polyps and especially the overwintering podocysts are more resistant to varying physical conditions (Peard 2002).

There are no known chemical control methods for this species.

Remarks: Freshwater jellyfish are not considered dangerous to humans.  Although its stings can paralyze macroinvertebrates and small fish, its small nematocysts are not likely to penetrate human skin (Peard, 2002).

Populations of C. sowerbyi are frequently all male or all female, making sexual reproduction rare (Pennak, 1989).

Pennak (1989) gives several useful line drawing of C. sowerbyi.  For an illustrated description of the lifecycle, see Thorp and Covich (1991), or visit Sexual Reproduction in Freshwater Jellyfish (Sasaki, 1999).

References (click for full reference list)

Author: McKercher, E., O; Connell, D., Fuller, P., Liebig, J., Larson, J., Makled, T.H., Fusaro, A., and Daniel, W.M.

Contributing Agencies:

Revision Date: 5/18/2021

Citation for this information:
McKercher, E., O; Connell, D., Fuller, P., Liebig, J., Larson, J., Makled, T.H., Fusaro, A., and Daniel, W.M., 2023, Craspedacusta sowerbyi Lankester, 1880: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 5/18/2021, Access Date: 12/1/2023

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.