Bythotrephes longimanus

Common Name: Spiny waterflea

Synonyms and Other Names:

Formerly known as Bythotrephes cederstroemii (Berg and Garton, 1994; Yan and Pawson, 1998; Berg et al., 2002; Therriault et al., 2002).  spiny water-flea

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Identification: Bythotrephes longimanus is a large cladoceran distinguished by a long straight tail spine that is twice as long as its body and has one to three pairs of barbs. Parthenogenically produced animals have kink in middle of their spine and sexually produced animals lack the kink. Bythotrephes appearance is similar to Cercopagis pengoi, another Great Lakes invader, except Bythotrephes is larger with a more robust spine that lacks a hook at the end.

Size: can reach 15 mm

Native Range: Northern Europe and Asia

Great Lakes Nonindigenous Occurrences: Bythotrephes was first detected in December 1984 in Lake Huron (Bur et al., 1986), then Lake Ontario in September 1985 (Lange and Cap, 1986), Lake Erie in October 1985 (Bur et al., 1986), Lake Michigan in September 1986 (Evans, 1988), and Lake Superior in August 1987 (Cullis and Johnson, 1988).


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 Bythotrephes longimanus are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IL198620112Lake Michigan; Little Calumet-Galien
IN198619881Lake Michigan
MI1984201712Betsie-Platte; Betsy-Chocolay; Dead-Kelsey; Keweenaw Peninsula; Lake Huron; Lake Michigan; Lake Superior; Michigamme; Ontonagon; Pere Marquette-White; St. Marys; Thunder Bay
MN198720184Baptism-Brule; Cloquet; Lake Superior; St. Louis
NY198520195Lake Champlain; Lake Erie; Lake Ontario; Mettawee River; Oneida
OH198520191Lake Erie
PA199820021Lake Erie
VT201420141Lake Champlain
WI198620188Bad-Montreal; Beartrap-Nemadji; Door-Kewaunee; Lake Michigan; Lake Superior; Lower Fox; Menominee; St. Louis

Table last updated 4/25/2024

† Populations may not be currently present.

Ecology: Bythotrephes longimanus is found among the zooplankton in the upper water column of large and small temperate lakes. They can tolerate brackish water, and are most abundant in late summer and autumn. Occurrence and density of Bythotrephes populations are determined mainly by water temperature and salinity; Bythotrephes is limited to regions where water temperature ranges between 4 and 30°C and salinity is between 0.04 and 8.0 parts per thousand, but it prefers temperature between 10 and 24°C and salinity between 0.04 and 0.4 ppt (Grigorovich et al. 1998). Temperature plays a major role in determining the abundance and location of Bythotrephes in the Great Lakes, as they prefer cooler water and cannot tolerate very warm lake temperatures (Berg and Garton 1988, Garton et al. 1990, Brown and Branstrator 2004). Bythotrephes occurs in oligotrophic and mesotrophic lakes and has a lower tolerance to low dissolved oxygen concentrations than the native cladoceran Leptodora kindtii (Sorensen and Branstrator, 2017). Bythotrephes can reproduce both asexually and sexually; unfertilized eggs are carried in a brood pouch, and fertilized eggs are cast in the fall, hatching the following spring (Evans, 1988). The intensity and type of predation pressure appears to affect the size of Bythotrephes, its spine length, and the extent of its diel migrations (Straile and Halbich, 2000).

Bythotrephes longimanus is a visual predator, using its large compound eye to detect zooplankton (Azan et al., 2015). They consume 75% of their body weight each day in prey items (Lehman et al., 1997).

Means of Introduction: Bythotrephes was probably introduced from ship ballast water (Sprules et al. 1990, Berg et al. 2002) and possibly as diapausing eggs from sediment in ballast tanks (Evans 1988). 

Status: Bythotrephes is established in all of the Great Lakes and many inland lakes in the region. Densities are very low in Lake Ontario, low in southern Lake Michigan and offshore areas of Lake Superior, moderate to high in Lake Huron, and very high in the central basin of Lake Erie (Barbiero et al., 2001; Vanderploeg et al., 2002; Brown and Branstrator, 2004).

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


Bythotrephes longimanus has a high environmental impact in the Great Lakes.

Bythotrephes reproduce rapidly and consume small zooplankton such as small cladocerans, copepods, and rotifers, potentially competing directly with planktivorous larval fish for food (Berg and Garton, 1988; Evans, 1988; USEPA, 2008; Vanderploeg et al., 1993). At times, its consumption may even exceed that of zooplankton production (Bunnell et al., 2011).

A decline in native cladocerans following the introduction of Bythotrephes has been observed in Lake Huron and Lake Michigan (Barbiero and Tuchman, 2004). In Lake Erie, the detection of Bythotrephes in 1985 was also accompanied by a decline in multiple species of cladocerans (e.g., Eubosmina coregoni, Daphnia mendotae, D. retrocurva), including an almost complete absence of Diaphanosoma spp. wherever Bythotrephes was present in 1986 (Barbiero and Rockwell, 2008). This study further documented a lack of spatial overlap between Bythotrephes and Leptodora (a native water flea). This is in concordance with many other studies which have documented a negative correlation between abundance of the two species, implying that competition and/or predation from Bythotrephes has played a significant role in declines of Leptodora (e.g., Branstrator, 1995; Fernandez et al., 2009; Foster and Sprules, 2009; Garton et al., 1990; Lehman and Cáceres, 1993; Yan and Pawson, 1997). Interestingly, Leptodora coexists with and often outnumbers Bythotrephes in European lakes, which could be due to higher abundance of available zooplankton prey or lower levels of planktivory in combination with the greater conspicuousness of Bythotrephes (Foster and Sprules, 2009). In Lake Michigan, the decline of D. retrocurva and D. pulicaria populations in contrast to relatively stable populations of D. mendotae has been attributed to the latter’s markedly faster escape responses (Pichlová-Ptácníková and Vanderploeg, 2011).

Some studies have documented an increase in chlorophyll a abundance with the invasion of Bythotrephes, potentially due to a release from grazing following increased predation pressure on zooplankton species (Barbiero and Rockwell, 2009; Hovius et al., 2007). This would imply that Bythotrephes is capable of affecting multiple trophic levels of the freshwater community. However, an increase in Bythotrephes abundance is not always correlated with an increase in chlorophyll a (Foster and Sprules, 2009; Strecker and Arnott, 2008). Notably, Strecker and Arnott (2008) demonstrated that invaded lakes experienced a significant reduction in secondary production, and hence a reduction in resources available in the epilimnion.

In some cases, Bythotrephes has been associated with a shift in cladoceran communities towards larger taxa over small possibly due to Bythotrephes predation of smaller species (Barbiero and Rockwell, 2008; Hovius et al., 2007; Yan and Pawson, 1997). Yet not all of Bythotrephes’ effects can be attributed to direct consumption. Vertical migration has also been observed in Daphnia spp. and copepod (e.g., Diacyclops thomasi, Leptomdiaptomus ashlandi, L. minutus) populations following Bythotrephes invasion, indicating that some species may migrate to deeper waters during the day to avoid Bythotrephes predation or competition (Bourdeau et al., 2011; Jokela et al., 2011; Lehman and Cáceres, 1993). Diel vertical migration may lead to an indirect negative effect on these native prey species, including reduced individual and population growth rates at lower temperatures (Pangle and Peacor, 2006; Pangle et al., 2007).

Meanwhile, the invasion of Bythotrephes has evidently had little or no negative effects on mysids (Foster and Sprules, 2009; Nordin et al., 2008) and rotifers (Barbiero and Warren, 2011; Hovius et al., 2007), and has sometimes been associated with increases in these populations. Bythotrephes has been implicated as a factor in the decline of alewife (Alosa pseudoharengus) in Lakes Ontario, Erie, Huron, and Michigan (Evans, 1988). However, recent studies suggest that Bythotrephes is a significant and even preferred prey item of alewife (Pothoven et al., 2007; Stewart et al., 2009).

Significant increases in the trophic position of zooplankton (reduced herbivorous cladoceran biomass and increased omnivorous/predatory copepod biomass) and planktivorous fish such as the lake herring (Coregonus artedi) with the introduction of Bythotrephes has the potential to lead to substantial contaminant biomagnification in consumers (Rennie et al., 2011). However, increased mercury concentrations in consumers has not been observed following invasion; this may be attributed to increased increased foraging and growth efficiencies of consumers or to changes in the feeding habits of omnivorous prey (Rennie et al., 2011).

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

The first noticeable impact of Bythotrephes was on fishermen. The tail spines of Bythotrephes hook on fishing lines, fouling fishing gear. This problem has largely been eliminated with a switch to line/gear types less susceptible to Bythotrephes fouling.

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

Bythotrephes is a food source for fish including yellow perch, white perch, walleye, white bass, alewife, bloater chub, Chinook salmon, emerald shiner, spottail shiner, rainbow smelt, lake herring, lake whitefish, and deepwater sculpin (Branstrator and Lehman, 1996; Bur et al., 1986; Makarewicz and Jones, 1990). However due to its long tail spine, predation of Bythotrephes is mainly restricted to larger fish and non-gape limited species (Pothoven et al., 2007).

There is speculation that Bythotrephes may control the abundance of Cercopagis pengoi through competition and predation (Vanderploeg et al., 2002).

Management: Regulations (pertaining to the Great Lakes)
In Wisconsin, the spiny waterflea is a prohibited invasive species (Wis. Admin. Code § NR 40.04), which indicates that it is likely to survive and spread if introduced into the state, potentially causing economic or environmental harm or harm to human health (Wis. Admin. Code § NR 40.02). With certain exceptions, it is unlawful to transport, possess, transfer or introduce a prohibited invasive species in Wisconsin (Wis. Admin. Code § NR 40.04). In Minnesota, the spiny waterflea is a regulated invasive species (Min. Admin. Rules § 6216.0260). It is legal to possess, sell, buy, and transport regulated invasive species, but no person may introduce a regulated invasive species without a permit (Min. Admin. Rules § 6216.0265 Subpart 1).

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

Like the confamilial fishhook waterflea (Cercopagis pengoi), the spiny waterflea is most likely to be spread on aquatic equipment, especially fishing lines. Consequently, public education is a significant method of control which can greatly reduce incidences of species transfer by unaware or incautious anglers (Jacobs and MacIsaac, 2007; Lui et al., 2010).

Bythotrephes longimanus is consumed by rainbow smelt, lake herring, lake whitefish, yellow perch, white perch, white bass, walleye, alewife, bloater chub, emerald shiner, spottail shiner, deepwater sculpin, and chinook salmon in the Great Lakes (Bur et al., 1986; Makarewicz and Jones, 1990; Branstrator and Lehman, 1996). Bythotrephes longimanus’ defensive tailspine has been observed increasing in size throughout the summer in response to predation pressure (Straile and Halbich, 2000). Consequently, larger fish are more likely to be successful predators (Branstrator and Lehman, 1996).  The opossum shrimp (Mysis relicta) has been observed eating B. longimanus in Ontario lakes, but the frequency of consumption appeared related to abundance of the invader and alternate prey (Nordin, 2008).

Bythotrephes longimanus collects in gelatinous clumps on fishing lines, downrigger cables, and other aquatic equipment (Lui et al., 2010). Responsible maintenance and cleaning methods are recommended to prevent spread between water bodies, including cleaning all aquatic equipment with high pressure (>250 psi) or hot (>50°C) water after each use (Ontario’s Invading Species Awareness Program). The acute upper lethal temperature level for B. longimanus, at which death occurs rapidly, is 40°C (GLMRIS, 2012), and a study found that B. longimanus specifically requires 10 minutes treatment with 43°C water to ensure 100% mortality (Beyer et al., 2011). Fishing lines designed specifically to prevent the spread of waterfleas, such as the Flea Flicker brand, have been proven effective in significantly reducing fouling on lines, indicating their importance as a management tool (Jacobs and MacIsaac, 2007).

Electron beam irradiation has been used to control microorganisms in aquatic pathways, including Bythotrephes longimanus (GLMRIS, 2012). Electron beam irradiation is a non-selective control method which exposes water to low doses of radiation using gamma-sterilizers or electron accelerators, breaking down DNA in living organisms while leaving behind no by-products (GLMRIS, 2012). Ultraviolet (UV) light can also effectively control microorganisms including B. longimanus in water treatment facilities and narrow channels, where UV filters can be used to emit UV light into passing water, penetrating cell walls and rearranging DNA of microorganisms (GLMRIS, 2012).

There are no known chemical control methods for this species

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

Remarks: Deweese et al (2021) report on preliminary microfossil evidence for the presence of Bythotrephes in 4 inland lakes of the Great Lakes region which would place the introduction dates for this species signficantly earlier.  The authors still speculate whether the data may be an artefact (albeit of a common method), and should be considered preliminary at best. If these corroborated, earliest dates of reported microfossils should be 1934 (Lake Kabetogama, MN), 1908 (Mille Lacs, MN), 1900 (Lake Nipissing, Ontario) and 1650s (Three Mile Lake, Ontario).  Such early records call into question both the presumed means of introduction for this species (ballast water) as well as the possibility that the species should be considered native.  

References (click for full reference list)

Author: Liebig, J., A. Benson, J. Larson, T.H. Makled, A. Fusaro, and K.M. Reaver

Contributing Agencies:

Revision Date: 10/6/2021

Citation for this information:
Liebig, J., A. Benson, J. Larson, T.H. Makled, A. Fusaro, and K.M. Reaver, 2024, Bythotrephes longimanus: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 10/6/2021, Access Date: 4/25/2024

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.