Gymnocephalus cernua (Linnaeus, 1758)

Common Name: Ruffe

Synonyms and Other Names:

Eurasian ruffe, blacktail, pope, redfin darter, river ruffe, Acerina cernua, Gymnocephalus cernuus

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Identification: The ruffe is a small fish, reaching 10 inches in length, is olive-brown to golden-brown on its back with yellowish white undersides. Its fused dorsal fins are characterized by 12–19 dorsal spines followed by 11–16 soft dorsal rays. The caudal fin has 16–17 rays. Distinguishing characteristics were provided by Wheeler (1969, 1978), Maitland (1977), Page and Burr (1991), McLean (1993), and Stepien et al. (1998). Detailed traits and an identification key to members of the genus were given by Holcik and Hensel (1974). Name given by some authors is Acerina cernua (e.g., Berg 1949), also Gymnocephalus cernuus (e.g., Page and Burr 1991).

Size: 25 cm

Native Range:
Northern Europe and Asia (Berg 1949; Holcik and Hensel 1974; Wheeler 1978; Page and Burr 1991).

Great Lakes Nonindigenous Occurrences: The ruffe was first identified by Wisconsin DNR in specimens collected from the St. Louis River at the border of Minnesota and Wisconsin in 1987 (Pratt 1988; Pratt et al. 1992; Czypinski et al. 1999, 2000, 2001, 2003). Following that report, reexamination of archived samples revealed misidentified larval specimens of ruffe had been collected from the same area in 1986 (Pratt 1988). The ruffe subsequently spread into Duluth Harbor in Lake Superior and several tributaries of the lake (Underhill 1989; Czypinski et al. 1999, 2000, 2004; Scheidegger, pers. comm.; J. Slade, pers. comm.). It is found in the Amnicon, Flag, Iron, Middle, Raspberry, and Bad rivers, Chequamegon Bay, and Apostle Islands National Lakeshore in Wisconsin (Czypinski et al. 1999, 2000, 2001, 2003, 2004; Tilmant 1999).  In August 1994, it was found in Saxon Harbor, Wisconsin, and in the upper peninsula of Michigan at the mouths of the Black and Ontonagon rivers (K. Kindt, pers. comm.). In the lower Peninsula of Michigan along Lake Huron, the first three specimens were caught at the mouth of the Thunder Bay River in August 1995 (K. Kindt, pers. comm.). This species has also been collected in Michigan in Lake Michigan, Lake Superior, Torch Lake, Little Bay de Noc in Escanaba, Big Bay de Noc, Misery River, Ontonagon River, Thunder Bay, and Sturgeon River Sloughs (Czypinski et al. 1999, 2000, 2001, 2003, 2004; A. Bowen, pers. comm.; Pearce, pers. comm.; Zorn, pers. comm.).  The ruffe has been collected in Lake Superior at Thunder Bay Harbour, Ontario, Canada (Czypinski et al. 1999, 2000, 2001, 2004, 2007).

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 Gymnocephalus cernua are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
MI1994202213Betsy-Chocolay; Black-Presque Isle; Cheboygan; Keweenaw Peninsula; Lake Huron; Lake Michigan; Lake Superior; Lone Lake-Ocqueoc; Ontonagon; St. Marys; Sturgeon; Thunder Bay; Waiska
MN198620173Beaver-Lester; Lake Superior; St. Louis
WI198620165Bad-Montreal; Beartrap-Nemadji; Lake Michigan; Lake Superior; St. Louis

Table last updated 6/26/2022

† Populations may not be currently present.

* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: The diet of ruffe changes throughout the course of development, becoming more benthic in nature with increasing size (Ogle et al. 2004). Copepoda, Daphnia spp., and Bosmina longirostrus dominated the overall diet of larval ruffe in the St. Louis Harbor (Ogle et al. 2004). Chironomids and the bottom-dwelling larvae of other insects, mainly mayflies and stoneflies, were frequently consumed in fresh water and, with increasing body size, became increasingly important in the diet of ruffe (Hölker and Thiel 1998). In laboratory experiments, Fullerton et al. (1998) found that ruffe preferred soft-bodied macroinvertebrates. Histological examination of ruffe from the Duluth-Superior Harbor population revealed that the spawning period extended from late April through mid-June in 1994 (Leino et al. 1997). Ruffe is often associated with bottom waters and can tolerate lacustrine and lotic systems and depths to 85 m (Sandlund et al. 1985). The species' intolerance to deeper waters may limit its range of potential suitable habitat to Lake Erie, southern Lake Michigan, and shallow waters of the other Great Lakes (U.S. EPA 2008).

Means of Introduction: The ruffe was probably introduced via ship ballast water discharged from a vessel arriving from a Eurasian port, possibly as early as 1982-1983 (Simon and Vondruska 1991; Ruffe Task Force 1992). Within the Great Lakes, the species' spread may have been augmented by intra-lake shipping transport (Pratt et al. 1992; Stepien et al. 1998). Recent genetic research has indicated that the origin of ruffe introduced to the Great Lakes was southern Europe, not the Baltic Sea as previously believed (Stepien et al. 1998).

Status: The ruffe has already invaded Lake Superior and GARP modeling predicts it will find suitable habitat almost everywhere in all five Great lakes. GARP models are not able to make a prediction about some of the deeper waters of Lake Superior (U.S. EPA 2008). It has been established in western portion of Lake Superior since about 1988 and expanded in an easterly direction. Ruffe has been reported from Lake Huron at Thunder Bay River, and in Thunder Bay, Lake Superior, Ontario, Canada. It has become the dominant species in the St. Louis River estuary (McLean 1993) and considered the most abundant of the 60 species found in Duluth Harbor (Ruffe Task Force 1992). Based on bottom trawl samples, ruffe makes up an estimated 80% of fish abundances in the southwestern regions of Lake Superior (Leigh 1998). The population in Duluth Harbor was estimated at two million adult fish in 1991 (Ruffe Task Force 1992). In 2006 surveys of Lake Huron, no ruffe were collected from Thunder Bay River and St. Marys River (Czypinski et al. 2007). In fact, ruffe has not been collected in the Thunder Bay region of Lake Huron since 2003 despite sampling efforts nor has it been found elsewhere in the lake (A. Bowen, pers. comm.).

Great Lakes Impacts: Gymnocephalus cernua has a moderate environmental impact in the Great Lakes.

Ruffe was first discovered in the St. Louis River, a tributary to western Lake Superior, in the mid 1980s; by 1991, it was the most abundant fish in this area (Bronte 1998). The increase in ruffe was concurrent with declines in several fish species, including yellow perch (Perca flavescens), emerald shiner (Notropis atherinoides), and trout-perch (Percopsis omiscomaycus) (Bronte 1998, McLean 1993). However, there was a lack of clear causal evidence between the two events (Bronte 1998).

There has been a great deal of concern that ruffe may have a detrimental effect on more desirable species in Lake Superior, including yellow perch and walleye (Sander vitreus), by feeding on the young of these species (Raloff 1992) or by competing with them for food (McLean 1993). In Lake Superior, consumption of cisco (Coregonus artedii) eggs by ruffe has been documented at a level which could impact the population over winter months (Selegby 1998). Ogle et al. (1995) studied the diet of introduced ruffe inhabiting the St. Louis estuary. Their findings indicated that the species preys heavily on benthic insects, thereby suggesting that ruffe competes for food with yellow perch, trout-perch, and other native benthic-feeding fishes.

Savino and Kolar (1996) conducted a laboratory study to test for food competition between ruffe and yellow perch. They found that competition could occur between the two species, but that the outcome was not always clear, as each species exhibited competitive advantages and disadvantages (Savino and Kolar 1996). Fullerton et al. (1998) also concluded that similarities in dietary preferences and feeding rates of ruffe and yellow perch suggest a strong possibility for interspecific competition.

Ruffe holds an advantage over native perch in its ability to better select moving objects under relatively dim light conditions or at high turbidity. Kolar et al. (2002) found that in a laboratory setting, ruffe exhibited higher consumption rates of benthic invertebrates in darkness over bare cobble and complex substrates than did yellow perch. With a very sensitive lateral line system and night-adapted vision, ruffe is more suited for foraging under poor light conditions than is yellow perch (Hölker et al. 1998).

Mayo et al. (1998) completed an assessment of an experimental top-down control system which sought to control ruffe populations with the stocking of five native predators (northern pike (Esox lucius), walleye, smallmouth bass (Micropterus dolomieu), brown bullhead (Ameiurus nebulosus), and yellow perch). The authors found that although predators consumed nearly half of available ruffe biomass in one year, each species preferentially selected native fish species and ruffe abundance continued to increase (Mayo et al. 1998). However, consumption of ruffe appeared to increase yearly for most native predators, suggesting that native species may learn to prey on ruffe over time (Mayo et al. 1998).

Ruffe exhibits rapid growth and high reproductive output, and adapts to a wide range of habitat types (McLean 1993); therefore the species may pose a threat to native North American fish. The ruffe has affected fish populations in other areas where introduced. In Scotland, native perch populations declined and, in Russia, whitefish numbers have declined because of egg predation by ruffe (McLean 1993).

Current research on the socio-economic impact of Gymnocephalus cernua in the Great Lakes is inadequate to support proper assessment.

When ruffe first invaded Lake Superior, it was thought that this species could generate a considerable cost for recreational fishing, particularly by causing a decline in yellow perch (Perca flavescens) populations (Leigh 1998). Under a moderate scenario of spread and impact, it was predicted that ruffe could generate costs in excess of $500 million by 2050 (Leigh 1998). However, these concerns have yet to be confirmed as the extent of ruffe’s contribution to declines in native fish populations remains undecided (Czypinksi et al. 2007). Ruffe abundance appeared to remain stable or decline annually in Lake Superior as late as 2001-2005 (Czypinski et al. 2007, Gorman et al. 2010).

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

Management: Regulations (pertaining to the Great Lakes)
Aquarium fish-keeping, production, keeping in captivity, breeding, stocking, transport, sale, or purchase of live ruffe is prohibited in Quebec under the Quebec Regulation Respecting Aquaculture and the Sale of Fish § RRQ, c C-61.1, r 7, Schedule IV.  In Ontario, ruffe is an invasive fish under Ontario Fishery Regulations § SOR/2007-237, and therefore may not be possessed without a license and shall not be used or possessed for use as baitfish.

In Pennsylvania, it is unlawful to possess live ruffe or to import or introduce live ruffe to Pennsylvania waters under 58 PA Code § 71.6. It is unlawful to sell, purchase, offer for sale or barter for live ruffe under 58 PA Code § 63.46. Ruffe may not be transported from another state, province, or country into Pennsylvania, liberated into a Pennsylvania watershed, or transferred between Pennsylvania waters without written permission from the Pennsylvania Fish and Boat Commission under 58 PA Code § 73.1. In Ohio, it is unlawful to possess, import, or sell live individuals of ruffe except for research, education, or public display when authorized (Ohio Admin. Code § 1501:31-19-01). In Michigan, ruffe is a prohibited species under MI NREPA 451 § 324.41301. No person shall knowingly possess a live prohibited organism in Michigan except for education, research, or identification purposes as listed in MI NREPA 451 § 324.41303. It is also unlawful to introduce prohibited organisms in MI under MI NREPA 451 § 324.41305. In Michigan, a violation involving a prohibited species is a felony, and a knowing introduction violation with intent to harm is punishable with up to 5 yrs. imprisonment and a $2,000 to $1,000,000 fine (MI NREPA § 324.41309). In Indiana, ruffe is classified as an exotic fish under 312 IAC 9-6-7, meaning except as otherwise provided, no individual can import, possess, propagate, buy, sell, barter, trade, transfer, loan, or release into public or private waters live fish, recently hatched juveniles, viable eggs, or genetic material. In Illinois, ruffe is listed as an injurious species under Illinois Admin. Code 17 § 805.20. It is unlawful to possess, propagate, buy, sell, barter, or offer to be bought, sold, bartered, transported, traded, transferred, or loaned an injurious species to any person or institution unless a permit is obtained from the Illinois DNR (Illinois Admin. Code 17 § 805.30). In Wisconsin, ruffe is a restricted species as an established non-native, and therefore cannot be transported, possessed, transferred, or introduced without a permit (Wis. Admin. Code § NR 40.05). In Minnesota, ruffe is a prohibited invasive species, meaning it is unlawful (a misdemeanor) to possess, import, purchase, transport, or introduce an organism except under permit for control, research, or education (Minn. Admin. Rules § 6216.0250).

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

Minnesota and Wisconsin, with advice from the U.S. Fish and Wildlife Service, implemented a top-down control program for ruffe in the St. Louis River, western Lake Superior, in 1989, using northern pike (Esox lucius), walleye (Sander vitreus), smallmouth bass (Micropterus dolomieui), brown bullhead (Ameiruus nebulosus), and yellow perch (Perca flavescens) (Mayo et al. 1998). A bioenergetics modeling evaluation of the top-down control program revealed that although predators ate as much as 47% of ruffe biomass in one year, they avoided ruffe and were selective for native prey, and were thus unable to halt the increase in ruffe abundance (Mayo et al. 1998). However, the authors noted that northern pike and walleye appeared to have potential for top-down control of ruffe due to a combination of their diets and population sizes, and due to indications that they may learn to prey more selectively on ruffe (Mayo et al. 1998).

As Mayo et al. (1998) noted, caution is advised when considering top-down biological control as a management tool because the stability properties of a system do not just depend on predation, but also on the life histories of component species and their interactions.

There are no known physical control methods for this species.

Of the four chemical piscicides registered for use in the United States, antimycin A and rotenone are considered general piscicides, but no studies have been found of their effects on Gymnocephalus cernua (GLMRIS 2012).

Evaluation of the effects of common piscicides on ruffe revealed that the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) has potential for selective control of the species (Boogaard et al. 1996). Ruffe was 3 to 6 times more sensitive to TFM than both yellow perch (Perca flavescens) and brown trout (Salmo trutta) (Boogaard et al. 1996). Toxicity tests in May and August 1992 on the Brule River, Wisconsin revealed a 12h LC99.9 (concentration at which 99.9% of organisms are killed after 12 hours) of 5.9 mg/L at normal pH levels (~8.4) and 2.80 mg/L at low pH levels (Boogaard et al. 1996). Furthermore, at low pH levels (7.7-7.9) 12h LC25’s of 7.2 mg/L and 4.6 mg/L were recorded for yellow perch and brown trout, respectively, but at normal pH levels no brown trout or yellow perch mortality was recorded at the highest tested concentration of 8.8 mg/L (Boogaard et al. 1996). A cost benefit analysis of a U.S. ruffe control program supported TFM as a promising chemical control (Leigh 1998). However, Dawson et al. (1998) suggest that TFM may have more application for treating entire bodies of water rather than localized areas because it tended to repel ruffe in preference tests, allowing them to move to untreated areas. Bottom-release formulations of bayluscide and antimycin showed promise for effectiveness in treating localized concentrations of ruffe, but more field testing is needed (Dawson et al. 1998).

Increasing CO2 concentrations, either by bubbling pressurized gas directly into water or by the addition of sodium bicarbonate (NaHCO3) has been used to sedate fish with minimal residual toxicity, and is a potential method of harvesting fish for removal, though maintaining adequate CO2 concentrations may be difficult in large/natural water bodies (Clearwater et al. 2008). CO2 is approved only for use as an anesthetic for cold, cool, and warm water fishes the US, not for use as euthanasia, and exposure to NaHCO3 concentration of 142-642 mg/L for 5 min. is sufficient to anaesthetize most fish (Clearwater et al. 2008).

It should be noted that chemical treatment will often lead to non-target kills, and so all options for management of a species should be adequately studied before a decision is made to use piscicides or other chemicals. Potential effects on non-target plants and organisms, including macroinvertebrates and other fishes, should always be deliberately evaluated and analyzed. The effects of combinations of management chemicals and other toxicants, whether intentional or unintentional, should be understood prior to chemical treatment. Boogaard et al. (2003) found that the lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2’,5-dichloro-4’-nitrosalicylanilide (niclosamide) demonstrate additive toxicity when combined. In another study on cumulative toxicity, combinations of Bayer 73 (niclosamide) and TFM with contaminants common in the Great Lakes (pesticides, heavy metals, industrial organics, phosphorus, and sediments) were found to be mostly additive in toxicity to rainbow trout, and one combination of TFM, Delnav, and malathion was synergistic, with toxicity magnified 7.9 times (Marking and Bills 1985). This highlights the need for managers to conduct on-site toxicity testing and to give serious consideration to determining the total toxic burden to which organisms may be exposed when using chemical treatments (Marking and Bills 1985). Other non-selective alterations of water quality, such as reducing dissolved oxygen levels or altering pH, could also have a deleterious impact on native fish, invertebrates, and other fauna or flora, and their potential harmful effects should therefore be evaluated thoroughly.

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

Remarks: The ruffe also has been collected in the Canadian waters of Lake Superior at Thunder Bay and in Kaministiquia River estuary, 290 kilometers northeast of Duluth. Seven fish were collected from the latter location in 1991 (Ruffe Task Force 1992). Busiahn (1993) indicated that the potential North American range of ruffe may well extend from the Great Plains to the eastern seaboard and north into Canada. However, early reports that the ruffe was established in Lake Michigan (e.g., Page and Burr 1991) are considered erroneous. In March 1997, an international symposium was held in Ann Arbor, Michigan, to exchange information on the biology and management of ruffe (Jensen 1997). Ogle et al. (1996) found that certain native species preyed on introduced ruffe; however, their study indicated that predation is unlikely to effectively prevent ruffe from colonizing new areas in the Great Lakes.

Brazner et al. (1998) found that densely vegetated shoreline wetland habitats provide a refuge from intense competition with ruffe for indigenous fish.

Since the last ITIS update and 2004 American Fisheries Society names list update, there has been a return to the original species epithet (cernua). Authorities such as Eschmeyer's Catalog of Fishes (30 Sept. 2011 update), the Peterson fish guide, have FishBase reflect this change. According to W. Eschmeyer (pers. comm.), "cernua" is a noun and so does not decline (i.e., not an adjective to match the masculine genus). The ITIS expert for this species also confirmed the valid species name is now G. cernua (W. Starnes pers. comm.), although ITIS has yet to reflect that change.

References: (click for full references)

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Boogaard, M.A., T.D. Bills, and D.A. Johnson. 2003. Acute toxicity of TFM and a TFM/niclosamide mixture to selected species of fish, including lake sturgeon (Acipenser fulvescens) and Mudpuppies (Necturus maculosus), in Laboratory and Field Exposures. Journal of Great Lakes Research 29(Supplement 1):529-541.

Boogaard, M.A., T.D. Bills, J.H. Selgeby, and D.A. Johnson. 1996. Evaluation of piscicides for control of ruffe. North American Journal of Fisheries Management 16(3):600-607.

Bowen, A. – U.S. Fish and Wildlife Service, Alpena Fish and Wildlife Conservation Office, Alpena, Michigan.

Brazner, J.C., D.K. Tanner, D.A. Jensen, and A. Lemke. 1998. Relative abundance and distribution of ruffe (Gymnocephalus cernuus) in a Lake Superior coastal wetland fish assemblage. Journal of Great Lakes Research 24 (2): 293-303.

Bronte, C.R., L.M. Evrard, W.P. Brown, K.R. Mayo, and A.J. Edwards. 1998. Fish community changes in the St. Louis River estuary, Lake Superior, 1989-1996: is it ruffe or population dynamics? Journal of Great Lakes Research 24(2):309-318.

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Clearwater, S.J., C.W. Hickey, and M.L. Martin. 2008. Overview of potential piscicides and molluscicides for controlling aquatic pest species in New Zealand. Science & Technical Publishing, New Zealand Department of Conservation, Wellington, New Zealand.

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Czypinski, G.D., A.K. Hintz, M.T. Weimer, and A. Dextrase. 2001. Surveillance for ruffe in the Great Lakes, 2000. U.S. Fish and Wildlife Service, Ashland, WI. 32 pp.

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Author: Fuller, P. G. Jacobs, J. Larson, T.H. Makled, and A. Fusaro

Contributing Agencies:

Revision Date: 11/26/2019

Peer Review Date: 5/13/2014

Citation for this information:
Fuller, P. G. Jacobs, J. Larson, T.H. Makled, and A. Fusaro, 2022, Gymnocephalus cernua (Linnaeus, 1758): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 11/26/2019, Peer Review Date: 5/13/2014, Access Date: 6/30/2022

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.