Dikerogammarus villosus (Sowinsky, 1894)

Common Name: Killer shrimp

Synonyms and Other Names:

Dikerogammarus villosus bispinosus Martynov, Gammarus villosus

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Identification: Dikerogammarus villosus has a laterally compressed, curled, semi-transparent body consisting of a head (cephalon), thorax (pereon), and abdomen. Its head contains one pair of eyes, mouthparts with relatively large and powerful mandibles, and two pairs of antennae, each with peduncle (broad stalk, connected to head) and flagellum (narrow, outer tip). Its pereon consists of seven segments, each with a pair of walking legs (pereopods)—the first four pairs extending downward and forward and the last three pairs extending downward and backward. In females, extra branches that serve as space to shelter eggs are present on the walking legs. Its abdomen consists of six segments divided into two three-segment parts: pleosome (anterior) with brush-like limbs known as pleopods, and urosome (posterior) with shorter, immobile rod-like limbs called uropods. This species’ body coloration can range from transparent and striped to a uniform dark pigmented color; however, the most frequent coloration pattern is a light spot or stripe on each segment against a dark background (Nesemann et al. 1995; Devin et al. 2001). Newly released young resemble adults but are microscopic in size.

This species can be distinguished from other Dikerogammarus species by the high, conical protuberances on its urosomes. In larger males (> 16mm), these bumps are tipped with three to five spines. Moreover, the second (lower) antennae have a sparsely haired peduncle and a flagellum with dense ‘brush-like’ tufts of setae (MacNeil et al. 2010).

Size: Up to 30 mm (Nesemann et al. 1995).

Native Range: Ponto-Caspian basin. Widely distributed in the lower reaches of the Danube River system in the region of Eastern Europe/Ukraine. Its original distribution was restricted to the lower Danube by the narrow valley of the Dunakanyar near the confluence of the Danube and Ipoly Rivers (Nesemann et al. 1995).

Nonindigenous occurrences: Widespread across Europe, including the catchments of the Baltic, North, and Mediterranean seas (Bij de Vaate et al. 2002; Jazdzewski et al. 2004). Reported in the following countries: Austria (Mayer et al. 2008), the Netherlands (Bij de Vaate & Klink 1995), Belgium (Messiaen et al. 2010), France (Devin et al. 2004), Italy (Castelatto et al. 2006), England (Macneil et al. 2010), Lithuania (Arbaciauskas et al. 2017), and Turkey (Rewicz et al. 2016).

This species is not currently in the Great Lakes region but may be elsewhere in the US. See the point map for details.

Ecology: Dikerogammarus villosus inhabits fresh/brackish water, lakes, rivers, and canals in areas with low current velocity. It can adapt to a wide variety of substrates as well as a wide range of temperature, salinity, and oxygen levels. This species attaches itself to fastened banks, sheet-pile walls, and surface algae mats and can inhabit any substrate except sand (Kobak et al. 2015). It can also anchor itself within deep rock pools and under porous stones (Nesemann et al. 1995). It prefers flows <10 cm/s and avoids flows >15 cm/s (Kobak et al. 2017). In the lower Rhine, this species reaches its highest densities on hard substrates, primarily boulders, rocks, and pebbles within 3 meters of the shoreline (Kelleher et al. 1998; Platvoet et al. 2009). Different size classes of individuals tend to separate spatially, with the smallest individuals typically found on roots or macrophytes and larger individuals found in cobble (Mayer et al. 2008). In river sections of high habitat complexity, D. villosus is able to coexist with other species of gammarids (Kley and Maier 2005).

This species is able to tolerate temperatures from 0–35°C, with an optimal temperature range of 5-15°C (Bruijs et al. 2001; Wijnhoven et al. 2003; van der Velde et al. 2009; Maazouzi et al. 2011). The lethal temperature for D. villosus was 30.0±0.9°C in hypoxic conditions (95kpa O2) and 32.3±0.7°C in normoxic (20 kpa O2) conditions (Verberk et al. 2018). It is not known to survive in waters warmer than 35°C and may not typically survive prolonged exposure to temperatures in excess of 27°C (Bruijs et al. 2001; Maazouzi et al. 2011). Females appear to have a higher thermal maximum than males. In a tank with a thermal gradient of 0–40°C, D. villosus females had a preference for waters >30°C and males had no preference. However, males infected with Cucumispora dikerogammari (a microsporidian parasite hypothesized to increase temperature preference of hosts) significantly chose warmer waters (>30°C) than uninfected males (Rachaleweski et al. 2018). Some disparity in reported temperature tolerance for this species could be attributed to the two genetically distinct populations of D. villosus that occur in Europe. The western population has a higher temperature range and the eastern population is more sensitive to sudden changes in temperature. However, there is potential for a new “super-hybrid” to form from the two populations that could havean even wider range of thermal tolerance (Hupalo et al. 2018).

It naturally occurs at 17 ppt but can tolerate salinities ranging from 0 to 20 ppt (Bruijs et al. 2001; Grigorovich et al. 2003). While able to survive short exposure (3 hours) to full strength seawater, D. villosus experiences 100% mortality when exposed to 34 PSU (practical salinity units) for 24 hours (Santagata et al. 2008). The lethal minimum oxygen concentration for this species is 0.380 mg O2/L; while such conditions are considered hypoxic, other Ponto-Caspian amphipods invaders in the Baltic Sea can tolerate even lower oxygen concentrations (Dedyu 1980). This species is sensitive to ammonia concentrations and incurs increased metabolic costs at 0.042 mg/L and dies within 4 hours at 98.0 mg/L (Normant-Saremba et al. 2015). Lake Erie is likely the only Great Lake that may reach the lower end of the aforementioned ammonia concentration range (Dove and Chapra 2015).

Dikerogammarus villosus is an omnivorous predator of many macroinvertebrates, including other gammarids, and is also able to collect detritus and to filter out suspended algae (Mayer et al. 2008). It exhibits a cannibalistic nature by occasionally eating conspecific newborns and weak adults (Dick and Platvoet 2000; Dick et al. 2002; Platvoet et al. 2009). Moreover, D. villosus has been observed to kill or injure potential prey without consuming it (Dick et al. 2002).

This amphipod is reproductive year round in its native range (Devin et al. 2004). Mean fecundity is around 30 eggs per female; however, females can lay up to 194 eggs per clutch, giving this species the highest fecundity of the European gammarids (Devin et al. 2004, Kley and Maier 2003, 2006; Pöckl 2007). In winter, when water temperatures drop to between 5.5 and 10.5°C, females exhibit a growth rate between 2.2 and 2.9 mm/month, while males show a slower growth rate of about 1.3 to 1.6 mm/month. With warmer spring water temperatures of 14.5–22°C, there is no significant difference in growth rate between the two sexes, and D. villosus is able to grow 2.6 mm in two weeks (Devin et al. 2004). Based on these observed growth rates, D. villosus may reach sexual maturity in as little as one month in 20°C waters (Devin et al. 2004). Well-established populations exhibit a female-biased sex ratio, with females making up about 60% of a mature population. Possible reasons for this skewed ratio include males’ larger body size, which makes them more prone to fish predation, and the presence of feminizing bacteria (Devin et al. 2004).

Means of Introduction: Means of Introduction: Dikerogammarus villosus has a moderate probability of introduction to the Great Lakes (Confidence level: High).

Potential pathway of introduction: Transoceanic shipping (ballast water)

Dikerogammarus villosus is native to the Ponto-Caspian region, an invasion donor “hot spot”, and has expanded its range throughout Western Europe. Due to its high tolerance to varying levels of salinity, oxygen and temperature, D. villosus is considered a highly likely candidate for introduction to the Great Lakes through ballast water transport from European ships (Mills et al. 1993; Ricciardi and Rasmussen 1998; Maclsaac 1999; Bruijs et al. 2001; Dick and Platvoet 2001; Dick et al. 2002; Grigorovich et al. 2002). As a benthic amphipod, ballast water flushing and/or exchange may be ineffective unless individuals are exposed to full-strength seawater for at least 24 hours (Santagata et al. 2008).

It was reported to attach to submerged objects (i.e., boat hulls, neeting, scuba gear, buoys) and thus recreational boating has been identified as one of the key vectors leading to its spread in the UK and elsewhere (Bacela-Spychalska et al. 2013; Rewicz et al. 2014; Šidagyte et al. 2017).

Status: Status: Not established in North America, including the Great Lakes.

Dikerogammarus villosus has a high probability for establishment if introduced to the Great Lakes (Confidence level: Moderate).

Dikerogammarus villosus has not yet been recorded in the Great Lakes, but this species has a history of successful invasions throughout Europe (Devin et al. 2001). In addition to a physiology that facilitates ballast water transport (relatively wide temperature and salinity tolerance), this species possesses many advantageous life history traits conducive to successful invasions, including: short generation time, rapid growth rate, female-biased sex ratio, early sexual maturity, high fecundity, brooding, production of multiple generations per year, exceptional predatory and competitive capabilities, ecological plasticity, and large size compared to related species (Dick and Platvoet 2000; Bruijs et al. 2001 Bij de Vaate et al. 2002; Wijnhoven et al. 2003; Devin et al. 2004). These characteristics, combined with abundant potential food sources, make D. villosus a species expected to have high potential for spread if introduced to the Great Lakes ecosystem (Ricciardi and Rasmussen 1998; Dick and Platvoet 2000; MacIsaac et al. 2001; Dick et al. 2002; Grigorovich et al. 2003; Devin et al. 2003, 2004). Its propagule pressure during the shipping season (May-October) is likely to be high, as this period overlaps with D. villosus’ reproductive peak (May/June) (Pöckl 2009). Following introduction, this species is also likely to spread by hitchhiking on recreational gear, boats, or trailers, as was a probable vector for its introduction to Lake Garda, Italy (Casellato et al. 2006).

Sieracki et al. (2014) described D. villosus as having a high invasion probability in ports of all 5 Great Lakes and is predicted to become rapidly widespread once introduced (Sieracki et al. 2014). The dispersal rate of this species across Europe is similar to that of many other Ponto-Caspian invasive amphipods (e.g., Dikerogammarus haemobaphes), spreading across the entire European continent in roughly 50 years (Bij de Vaate et al. 2002). Its spread and establishment in Great Britain is attributed to genetic founder effects and enemy release as invading shrimp had no parasites or predators to inhibit their expansion relative to their native range (Arundell et al. 2015).

In its invaded range in Europe, D. villosus has highly variable and unpredictable individual activity patterns relative to indigenous gammarids (Gammarus fossarum, G. pulex, and G. roseli) which promotes its invasion success by coping with new environmental conditions (Bierbach et al. 2016). In a laboratory experiment, Dikerogammarus villosus relied on a potential predator's diet rather than its species as a cue to avoid predation, thus likely facilitating their recognition of allopatric predators and increasing survival in newly invaded habitat (Jermacz et al. 2017b). This species also sustains its growth rate despite long-term predator presence due to its highly efficient anti-predator strategies (Jermacz et al. 2017a), including a harder exoskeleton, better shelter utilization, aggregation techniques, and enhanced metabolic sustainability while minimizing oxidation damage (Jermacz and Kobak 2018; Mennen and Laskowski 2018; Jermacz et al. 2020). Dikerogammarus villosus also exhibits variable morphology and coloration (Nesemann et al. 1995), which could facilitate its concealment and establishment in new environments.

Climatic conditions (e.g., temperature, precipitation, seasonality) and abiotic factors (e.g., pollution, water temperature, salinity, pH, nutrient levels and current) relevant to the success of D. villosus in its native and introduced ranges are similar to those in the Great Lakes. Kurikova et al. (2016) lists D. villosus as having high invasive potential to the Great Lakes based on climate-match data with their native range. Kramer et al. (2017) reports intermediate values of niche centrality for D. villosus in the Great Lakes, which indicates that climate conditions often, but not completely overlapped with its predicted niche. This species also is able to greatly reduce its oxygen demand at temperatures around 1°C, making it likely to overwinter in the Great Lakes (Wijnhoven et al. 2003; Becker et al. 2016).

Increased water temperature as a result of climate change is likely to enhance breeding, as has been observed with its relative D. haemobaphes (Kititsyna 1980). Despite D. villosus having broad environmental tolerances, particularly with respect to high salinity, it is not known to survive in waters warmer than 35°C and may not typically survive prolonged exposure to temperatures in excess of 27°C (Bruijs et al. 2001; Wijnhoven et al. 2003; van der Velde et al. 2009; Maazouzi et al. 2011). In contrast, food intake increased significantly for females as temperatures increased from 15–25°C due to a decrease in food handling time, which suggests predation pressure may increase due to climate change (Pellan et al. 2016). Some disparity in reported temperature tolerances for this species could be attributed to the two genetically distinct populations of D. villosus that occur in Europe. The western population has a higher temperature range tolerance and the eastern is more sensitive to sudden changes in temperature. However, there is potential for a new “super-hybrid” to form the two populations that has an even wider range of thermal tolerance and would pose an even bigger invasion threat (Hupalo et al. 2018).

A strong ecological connection exists between D. villosus and other Great Lakes invaders from the Ponto-Caspian, such as Dreissena polymorpha; under the theory of “invasional meltdown,” it has been predicted that invasion of the D. villosus will be facilitated by these companion species (Ricciardi and Rasmussen 1998; Dick and Platvoet 2000, 2002; Devin et al. 2003). For instance, beds of D. polymorpha may facilitate establishment of this large amphipod by providing colonization substrate (Dick et al. 2002; Devin et al. 2003). Dreissena bugensis beds are also a food source and habitat for D. villosus (Verstijnen et al. 2019). This species is also chemically attracted to the waters scented by D. polymorpha and thus the mussels may facilitate their invasion and establishment into new areas (Rolla et al. 2019). In Lake Balaton, Hungary, it uses Phragmites australis leaves as substrate and food source (Karádi-Kovács et al. 2015).

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


Dikerogammarus villosus has the potential for high environmental impact if introduced to the Great Lakes.

Native to the lower Danube river system and Caspian Sea basin, D. villosus has recently invaded and spread throughout most of Western Europe, causing significant ecological disruption. The short generation time, rapid growth rate, early sexual maturity, high fecundity, female-biased sex ratio, and large size of D. villosus as compared to related species make it a species expected to outcompete native species for resources (Bij de Vaate et al. 2002; Dodd et al. 2014). Dikerogammarus villosus is a fierce predator and superior competitor. Its ability to eat and displace other amphipods has led to the prediction of a great reduction in amphipod diversity if introduced to a variety of North American freshwater habitats (Dick and Platvoet 2000). In the Netherlands, D. villosus has replaced many populations of the European native amphipod species Gammarus duebeni, as well as those of the North American invader G. tigrinus (Dick and Platvoet 2000). Similar evidence of the replacement of native G. tigrinus by invasive D. villosus was reported in the Lippe River, Germany (Schröder et al. 2015). Dikerogammarus villosus has displaced an additional Dikerogammarus invader (D. haemobaphes) in portions of the Danube and Rhine rivers (Müller et al. 2002). A few mechanisms have been observed through which D. villosus displaces other gammarids. Dikerogammarus haemobaphes and Pontogammarus robustoides perceive the chemical stimuli of D. villosus as a threat and avoid it. In contrast, D. villosus is attracted to their alarm cues and follows them, which displaces them further and can actually enhance their spread (Kobak et al. 2016; Rachalweski et al. 2019). The aggressive aggregation and exceptional anti-predatory behaviors of D. villosus also forces other gammarids from shelter (Jermacz et al. 2015) and often leads to their predation. For example, D. villosus displaces Gammarus pulex, G. fossarum, and G. roeselii from shelter which are subsequently consumed by the fishes Neogobius melanostomus and Proterorhinus semilunaris, both of which have invaded the Great Lakers (Beggel et al. 2016; Blonska et al. 2016; de Gelder et al. 2016). Consequently, if D. villosus invades the Great Lakes, it may outcompete native gammarids for shelter and lead to their eventual consumption by non-native gobies.

This species is a shredder and its role in breaking down organic matter is not clear as studies conflict on whether D. villosus is more or less efficient than native species. In a laboratory experiment, the replacement of indigenous amphipods by Dikerogammarus villosus resulted in a decrease in leaf litter composition and altered microbial community that could lead to effects on benthic food webs (Boeker and Geist 2015). Jourdan et al. (2016) reported similar results that D. villosus had significantly lower rates of leaf shredding. In contrast, Richter et al. (2018) found similar rates of shredding by D. villosus compared to native species in a semi-natural experiment (including group-keeping, hideouts, and no starvation) and proposed that previous studies underestimated shredding rates in their completely artificial experimental setups. In-situ mesocosm experiments also showed D. villosus to have remarkably high food consumption rates (0.38–1.27 mg mg-1 d-1, in dry mass/dry body mass) and was an efficient shredder (Worischka et al. 2018). Populations that underwent dispersal shredded 3 times the leaf material (and equal to the European naitve Gammarus fossarium) than resident populations of D. villosus, indicating that dispersal syndromes may contribute to leaf shredding rates (Little et al. 2019). Further, the presence of D. villosus reduced leaf shredding efficiencies of resident Gammarus spp. due to non-consumptive effects (fear responses) (MacNeil and Briffa 2019).

This species also consumes eggs or juvenile stages of small fish, causing potential concern for game fish populations if introduced to the Great Lakes. In laboratory experiments, D. villosus significantly consumed Salmo trutta larvae (4.5%) relative to the control, but did not consume their eggs (Taylor et al. 2017). Dikerogammarus villosus are prey for crayfish, including Procambarus virginalis and Pacifastacus leniusculus, but it in turn consumes their eggs and hatchlings and can diminish their populations (Roje et al. 2021). Similarly, D. villosus consumed early-stage amphibians (Rana temporaria and Xenopus laevis) resulting in a potentially destabilizing Type II functional response, which could eventually result in the extirpation of the amphibians (Warren et al. 2021). It is important to note that none of the aforementioned crayfish or amphibians are native to the Great Lakes, however, similar impacts could affect native crayfish and amphibians in the region. Dikerogammarus villosus may also support the spread of dressenid mussels. A D. polymorpha mussel was found attached to the chitin of D. villosus and thus the gammarid may contribute to the mussels' passive spread and be another vector of transmission (Kenderov 2017). Further, 11.78% of D. villosus sampled from Lake Constance, Germany were infested with D. polymorpha (Yohannes et al. 2017).

Of 47 invasive species in Europe, D. villosus ranked 5th in terms of relative ecological impact score (Dick et al. 2017). In the Czech Republic, D. villosus is reported as having massive environmental impacts but limited socioeconomic impacts (Pergl et al. 2016). Dikerogammarus villosus also was predicted to have serious direct and indirect negative environmental effects if introduced to the Great Lakes ecosystem (Dick et al. 2002). In contrast, D. villosus is predicted to not have major impacts on the food web of Lake Erie in respect to fish and negative impacts may be limited to a few benthic prey groups (Zhang et al. 2019). In support of this prediction, Hellman et al. (2017) found no significant negative long term impacts of D. villosus on the benthic communities of the River Rhine and Elbe River, Germany, and suggest that positive impacts are as likely as negative impacts and are determined by the community composition prior to invasion. Koester et al. (2018) add that abiotic environmental factors influence benthic community structure more than D. villosus in the River Rhine. Médoc et al. (2018) showed through laboratory experiments that the superior resource use of D. villosus relative to G. pulex was negated by the high availability of non-animal, alternative food sources (e.g., leaf litter). Despite this, the abundance of indigenous gammarids declined with the increased density of D. villosus in Lake Constance, Germany. The density of D. villosus explained 26% of benthic variability in the lake and thus exhibited a strong impact on the benthic communities (Gergs and Rothhaupt 2015). In conclusion, the long term impacts on benthic communities of D. villosus are quite complex, and if introduced to the Great Lakes may be variable between individual lakes and their respective environments and resource availability.

Dikerogammarus villosus is host to several microsporidian parasites that may become emerging diseases in other crustaceans following host introduction (Ovcharenko et al. 2010; Bacela-Spychalska et al. 2012). Recently, a novel microsporidian parasite was discovered in D. villosus in the invaded River Trent, UK that could pose a threat to native fauna (Bojko et al. 2015). Dikerogammarus villosus is also an intermediate host to Pomphorhynchus laevis and is considered the vector of its introduction into the River Rhine (Hohenadler et al. 2018).

There is little or no evidence to support that Dikerogammarus villosus has the potential for significant socioeconomic impacts if introduced to the Great Lakes.

The socio-economic impact of this species on invaded areas of Western Europe is largely unknown. However, the ability of this species to consume eggs or juvenile stages of small fish creates a potential concern for fishery populations (Taylor et al. 2017).

Dikerogammarus villosus has the potential for moderate beneficial impacts if introduced to the Great Lakes.

Dikerogammarus villosus has displaced populations of other invading amphipods in Europe, including D. haemobaphes (another potential Great Lakes invader) (Müeller et al. 2002).

Dikergamerious villosus may act as a biological control agent to some degree in the Great Lakes. In Lake Balaton, Hungary, it uses Phragmites australis leaves as substrate and as a food source (Karádi-Kovács et al. 2015). Also, the mechanical movements of D. villosus irritates Dreissena polymorpha causing the mussels to spend more time closed/narrowly open and thus disrupts normal filtration and respiration activity (Dzierzynska-Bialonczyk et al. 2019).

Dikerogammarus villosus may provide some ecological benefit to the Great Lakes. It is an effective diluent for infectious bird schistosome cercaria that cause swimmer's itch because it is a dead-end host for the parasite essentially stopping its life-cycle (Stanicka et al. 2021). While D. villosus may provide benefit as a likely food item for Great Lakes fishes, it is also predicted to have a positive effect on the nonindigenous white perch (Morone americana) by serving as an additional food item (Zhang et al. 2019).

Management: Regulations (pertaining to the Great Lakes region)

Dikerogammarus villosus is listed as an injurious species in Illinois and it is unlawful to possess, propagate, purchase, sell, baterer, transport, trade, loan, or release unless a permit is obtained 17 ILL. ADM. CODE CH. I, SEC. 805). It is prohibited in Michigan, making it unlawful to possess, introduce, import, sell or offer this species for sale as a live organism (Michigan's Natural Resources Environmental Protection Act (Part 413 of Act 451)). In Ohio, it is unlawful for any person to possess, import or sell live individuals of this species (Ohio Administrative Code 1501:31-19-01). It is a prohibited species in Wisconsin and one cannot transport, possess, transfer, or introduce this species without a permit (Chapter NR 40, Wis. Adm. Code). It is prohibited in Ontario, and is illegal to import, possess, deposit, release, transport, breed/grow, buy, sell, lease or trade (Invasive Species Act, 2015, S.O. 2015, c. 22 - Bill 37).

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.

While no prevention mechanism exists for intracontinental dispersion, mandatory ballast control and ballast filtration systems are being implemented to prevent further transcontinental dispersion. Shoreline treatment plants for ballast water are also being considered, although this could be a costly option (Crosier et al. 2011).

It is highly sensitive to fluoride toxicity, and is expected to have low invasion risk in freshwater systems with 1.5 mg F-/L (10x the average background level) (Gonzala et al. 2010). Carbonated water led to narcosis in all D. villosus specimens within a few seconds (Sebire et al. 2018).

Hot water and steam are highly effective at controlling D. villosus. Immersion in 40°C water for 10 seconds led to 100% mortality of D. villosus (Shannon et al. 2018). Alternatively, a 90°C hot water spray 10 cm away for a duration of 5 seconds resulted in 100% mortality of D. villosus (Bradbeer et al. 2021). Steam (>100°C) killed all D. villosus within 10 seconds and 3 broad-spectrum disinfectants killed all specimens within 120 seconds at the lowest dose (1%) and in 15 seconds for the highest dose (4%) (Bradbeer et al. 2020). However, all of these methods are likely to result in the death of many non-target organisms.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for physical and chemical control measures.

Remarks: Dikerogammarus bispinosus was originally described as a subspecies of D. villosus (Martynov 1925), but a more recent genetic study by Müller et al. (2002) demonstrated that these two taxa should be considered to be separate species.

Obesogammarus aralensis, listed by Grigorovich et al 2003 as having a high probability of invading the Great Lakes, is most likely a synonym for Dikerogammarus villosus.

References (click for full reference list)

Author: Dettloff K., G. Núñez, E. Baker, A.J. Fusaro, and A. Bartos

Contributing Agencies:

Revision Date: 1/3/2022

Citation for this information:
Dettloff K., G. Núñez, E. Baker, A.J. Fusaro, and A. Bartos, 2024, Dikerogammarus villosus (Sowinsky, 1894): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=3609&Potential=Y&Type=2&HUCNumber=, Revision Date: 1/3/2022, Access Date: 4/22/2024

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.