Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Gymnocephalus cernuus
(ruffe)

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Datasheet

Gymnocephalus cernuus (ruffe)

Summary

  • Last modified
  • 15 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Natural Enemy
  • Host Animal
  • Preferred Scientific Name
  • Gymnocephalus cernuus
  • Preferred Common Name
  • ruffe
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Chordata
  •       Subphylum: Vertebrata
  •         Class: Actinopterygii
  • Summary of Invasiveness
  • G. cernuus is well-suited as an invader species; it matures quickly (sometimes within 1 year), has a high reproductive capacity, spawns multiple times over an extended period, feeds on an assortment of prey, and...

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Pictures

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PictureTitleCaptionCopyright
Gymnocephalus cernuus, or 'Ruffe'; lateral view of adult.(Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitleAdult
CaptionGymnocephalus cernuus, or 'Ruffe'; lateral view of adult.(Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; lateral view of adult.(Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
AdultGymnocephalus cernuus, or 'Ruffe'; lateral view of adult.(Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of head - there are 5-10 spines on the preopercle. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitleHead
CaptionGymnocephalus cernuus, or 'Ruffe'; close-up of head - there are 5-10 spines on the preopercle. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of head - there are 5-10 spines on the preopercle. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
HeadGymnocephalus cernuus, or 'Ruffe'; close-up of head - there are 5-10 spines on the preopercle. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of dorsal fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitleDorsal fin
CaptionGymnocephalus cernuus, or 'Ruffe'; close-up of dorsal fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of dorsal fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Dorsal finGymnocephalus cernuus, or 'Ruffe'; close-up of dorsal fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; head-on view of adult. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitleHead-on view
CaptionGymnocephalus cernuus, or 'Ruffe'; head-on view of adult. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; head-on view of adult. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Head-on viewGymnocephalus cernuus, or 'Ruffe'; head-on view of adult. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of tail fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitleTail fin
CaptionGymnocephalus cernuus, or 'Ruffe'; close-up of tail fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of tail fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Tail finGymnocephalus cernuus, or 'Ruffe'; close-up of tail fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of pelvic fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitlePelvic fin
CaptionGymnocephalus cernuus, or 'Ruffe'; close-up of pelvic fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of pelvic fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Pelvic finGymnocephalus cernuus, or 'Ruffe'; close-up of pelvic fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of anal fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitleAnal fin
CaptionGymnocephalus cernuus, or 'Ruffe'; close-up of anal fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of anal fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Anal finGymnocephalus cernuus, or 'Ruffe'; close-up of anal fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of pectoral fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitlePectoral fin
CaptionGymnocephalus cernuus, or 'Ruffe'; close-up of pectoral fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; close-up of pectoral fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Pectoral finGymnocephalus cernuus, or 'Ruffe'; close-up of pectoral fin. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; lateral view of juvenile. Juveniles are similar to adults, but are less deep-bodied and the flank spots are bigger and more blotch-like. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
TitleJuvenile
CaptionGymnocephalus cernuus, or 'Ruffe'; lateral view of juvenile. Juveniles are similar to adults, but are less deep-bodied and the flank spots are bigger and more blotch-like. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
Copyright©John D. Lyons/Wisconsin Department of Natural Resources
Gymnocephalus cernuus, or 'Ruffe'; lateral view of juvenile. Juveniles are similar to adults, but are less deep-bodied and the flank spots are bigger and more blotch-like. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)
JuvenileGymnocephalus cernuus, or 'Ruffe'; lateral view of juvenile. Juveniles are similar to adults, but are less deep-bodied and the flank spots are bigger and more blotch-like. (Picture by kind permission of John D. Lyons/Wisconsin Department of Natural Resources http://wiscfish.org/)©John D. Lyons/Wisconsin Department of Natural Resources
Identifying characteristics of Gymnocephalus cernuus.
TitleIdentifying characteristics
CaptionIdentifying characteristics of Gymnocephalus cernuus.
Copyright©Minnesota Sea Grant
Identifying characteristics of Gymnocephalus cernuus.
Identifying characteristicsIdentifying characteristics of Gymnocephalus cernuus.©Minnesota Sea Grant

Identity

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Preferred Scientific Name

  • Gymnocephalus cernuus (Linnaeus, 1758)

Preferred Common Name

  • ruffe

Other Scientific Names

  • Acerina cernua Linnaeus, 1758
  • Acerina czekanowskii Dybowski, 1874
  • Acerina fischeri Eichwald, 1873
  • Acerina vulgaris Cuvier in Cuvier and Valenciennes, 1829
  • Gymnocephalus cernua Collete, 1963
  • Perca cernua Linnaeus, 1758

International Common Names

  • English: Eurasian ruffe; pope; river ruffe; stone-perch

Local Common Names

  • Czechoslovakia (former): jezdik
  • Denmark: horke
  • Finland: kiiski; kueski
  • France: brenilie; perche goujonniere
  • Netherlands: kulbaars
  • Norway: nork; steinpurke
  • Poland: jazgars
  • Romania: ghibort
  • Russian Federation: ersh; jorsch
  • Ukraine: josch; lorsh

Summary of Invasiveness

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G. cernuus is well-suited as an invader species; it matures quickly (sometimes within 1 year), has a high reproductive capacity, spawns multiple times over an extended period, feeds on an assortment of prey, and adapts to a wide variety of environments. They tolerate a wide range of salinities, water temperatures, dissolved oxygen concentrations, substrates, depths, lentic and lotic environments, eutrophic to oligotrophic conditions (Adams and Maitland, 1998; Hölker and Thiel, 1998; Kovac, 1998; Lehtonen et al., 1998; Ogle, 1998; Popova et al., 1998). They have a competitive advantage over other species by being particularly adept at detecting and capturing prey in low-light or high-turbidity conditions due to an extremely sensitive cephalic lateral line system and retinal tapetum lucidum (Janssen, 1997; Hölker and Thiel, 1998; Ogle, 1998), which also helps to avoid predation in low-light conditions (Mayo et al., 1998). G. cernuus also have a morphological predator defence that includes well-developed dorsal and anal spines, and enlarged preopercular spines (Ogle, 1998). Their potential for rapid population growth, coupled with the threat of competition for food and space with native species, and predation on fish eggs (Adams and Tippet, 1991; Adams and Maitland, 1998; Hölker and Thiel, 1998; Ogle, 1998; Selgeby, 1998) pose a serious threat to fisheries in areas where they invade. G. cernuus has been declared invasive in the Great Lakes of the USA and Canada (Ruffe Control Committee, 1999). In a survey conducted by Winfield et al. (1998) of 31 researchers in 19 European countries, 30% of respondents perceived G. cernuus to be a problem. Of those that perceived them as a problem, 75% were introduced populations whereas 25% were native populations. The countries where introduced G. cernuus was perceived as a problem included France, Germany (southern), and the UK (Northern Ireland, north-western England, northern Wales, and south-west Scotland). Countries where native G. cernuus were perceived as problematic were Estonia and Russia (Yorosland).

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Chordata
  •             Subphylum: Vertebrata
  •                 Class: Actinopterygii
  •                     Order: Perciformes
  •                         Suborder: Percoidei
  •                             Family: Percidae
  •                                 Genus: Gymnocephalus
  •                                     Species: Gymnocephalus cernuus

Notes on Taxonomy and Nomenclature

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Gymnocephalus cernuus is the accepted name (Rosch et al., 1996; Nelson et al., 2004) for this species, which is a member of the Class Actinopterygii, the Order Perciformes, the family Percidae, and the subfamily Etheostomatinae (Wiley, 1992). The genus Gymnocephalus contains four species: Gymnocephalus schraester is endemic to the deeper waters of the Danube basin and Black Sea estuaries; Gymnocephalus acerina is found in rivers flowing into the northern Black Sea; Gymnocephalus baloni is endemic to the fast-flowing waters of the Danube and Dnieper Rivers;and G. cernuus. The accepted common name for G. cernuus is ruffe; however, it is also known as Eurasian ruffe or river ruffe. In England it is know as stone-perch, or pope, in Russia as ersh or jorsch, in the Ukraine as iorzh or bubyr, in Romania as ghibort, in Poland as jazgarz, in Norway as nork or steinpurke, in the Netherlands as kulbaars, in Germany as kaulbarsch, in France as perche goujonniere or Brenilie, in Finland as kiiski or kueski, in Denmark as horke (Ogle, 1998). Originally named Perca cernua by Linnaeus in 1758 it has also been known as Acerina vulgaris, Acerina fischeri, and Acerina czekanowskii (Eschmeyer, 1998). More recently it was known as Acerina cernua and G. cernua (Collette, 1963).

Description

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G. cernuus is morphologically variable throughout its range. For example, Stepien et al. (1998) found significant differences in four meristic and morphological characters among different North American and Eurasian G. cernuus populations. Significant differences were found in the number of soft rays in the dorsal fin, the number of preopercular spines, the length of the anal fin, and the length of the caudal peduncle. In addition, Aleksandrova (1974) described ‘shallow-bodied’ and ‘deep-bodied’ forms of G. cernuus existing in the same stretches of the Dneiper River.

The body is oval in cross-section. The total length is typically less than 20 cm, but may (rarely) exceed 25 cm. The colour is olive-brown to golden-brown on its back with yellowish-white undersides. They have glassy eyes and are slimy when handled. The mouth is slightly down-turned. They have fused dorsal fins characterized by 12-19 dorsal spines followed by 11-16 soft dorsal rays. There is no notch between the spiny and soft-rays of the dorsal fin. Dark spots are found in the membranes between the rays of the dorsal fin. There are 4-7 anal fin rays and the first two rays are sharp spines. The caudal fin has 16-17 rays. The pectoral fin has 13-17 rays. There are 33-42 lateral line scales, with 10-18 scales below and 5-10 scales above the lateral line. There are 6-7 branchiostegal rays and 6-14 gill rakers on the first arch. There is one opercular spine and 7-16 preopercular spines. There are 31-36 vertebrae. Distinguishing characteristics were provided by Wheeler (1969), Maitland (1977)Page and Burr (1991) and Ogle (1998). Meristic and morphometric variability in G. cernuus from different waters and from different ecological forms from the same waterbody are described by Popova et al. (1998).

Sexual dimorphism in G. cernuus is present in some individuals, but they may differ between populations (Petlina, 1967). Opalatenko (1967) found that least body depth, head length, pelvic fin length, and upper lobe of the caudal fin length were greater in males than in females. Petlina (1967), as reported in Popova et al. (1998), found differences between the sexes in pelvic fin length, eye diameter, head length, body thickness, head depth through the middle of the eye, and preventral, prepectoral, and anal-caudal distance. However, Popova et al. (1998) suggest that sexual dimorphism is not pronounced and only during the period of spawning are females distinguishable from males by their enlarged belly.

Distribution

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G. cernuus are native to most European countries. They are not native to Spain, Portugal, western France, Norway, northern Finland, Ireland, Scotland, Italy, Greece, Croatia, Serbia, or Montenegro. They are native to most of the former USSR where they inhabit rivers, lakes and brackish sea coastal waters. In the north, the range extends nearly to the coast of the arctic sea and, south, to the Aral, Caspian, and Black seas (Popova et al., 1998). They occur throughout Siberia except they are not found in the Amur River, Lake Baikal, and Transcaucasia (Berg, 1949; Holcik and Hensel, 1974; Popova et al., 1998). G. cernuus have been introduced to many European waters where they were not native and to the North American Great Lakes. In Europe they are now found in Loch Lomond, Scotland (Maitland et al.,1983), Llyn Tegid (Bala Lake), Wales (Winfield, 1992), Bathenthwaite Lake, England (Winfield, 1992), Lake Geneva, Switzerland and France, (Matthey, 1966), Lake Constance, on the borders of Austria, Germany and Switzerland (Rosch and Schmid, 1996), Lake Mildevatn, Norway (Kalas, 1995), the Camargue region, France (Ogle, 1998), and Italy (Chiara, 1986). In the North American Great Lakes they are found in Lake Superior, Lake Huron, and Lake Michigan (Simon and Vondruska, 1991; Pratt et al., 1992; Gunderson et al., 1998). Bordering these lakes are the USA states of Minnesota, Wisconsin, and Michigan, and the Canadian province of Ontario. They were first observed in the Great Lakes in Duluth-Superior Harbour of western Lake Superior in 1987 (Pratt et al., 1992).


Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

AfghanistanPresentNative Not invasive Coad, 1981
ChinaPresentNative Not invasive Walker Yang, 1999
IranPresentNative Not invasive Coad, 1995
UzbekistanPresentNative Not invasive Kamilov and Urchinov, 1995

North America

CanadaLocalisedIntroduced1989 Invasive Coad et al., 1995
-OntarioLocalisedIntroduced1989 Invasive Coad et al., 1995
USALocalised Invasive Welcomme, 1988
-MinnesotaLocalisedIntroduced1987 Invasive Pratt et al., 1992
-WisconsinLocalisedIntroduced1987 Invasive Pratt et al., 1992

Europe

AustriaPresentNative Not invasive Muus and Dahlström, 1968
BelgiumPresentNative Not invasive Muus and Dahlström, 1968
BulgariaPresentNative Not invasive Muus and Dahlström, 1968
CroatiaPresentNative Not invasive Gerstmeier and Romig, 1998
Czech RepublicPresentNative Not invasive Muus and Dahlström, 1968
DenmarkPresent Not invasive Muus and Dahlstrøm, 1990
EstoniaPresentNative Not invasive World Wide Web Electronic Publication, 1999
FinlandPresentNative Not invasive Koli, 1990
FrancePresentNative Not invasive Winfield et al., 1998; Keith and Allardi, 2001Introduced and invasive in northern France
GermanyPresentNative Not invasive Muus and Dahlström, 1968; Winfield et al., 1998Introduced and invasive in Lake Constance, 1987
HungaryPresentNative Not invasive Muus and Dahlström, 1968
ItalyPresentIntroduced Invasive Gandolfi et al., 1991
LatviaPresentNative Not invasive Winkler et al., 2000
LithuaniaPresentNative Not invasive Winkler et al., 2000
NetherlandsPresentNative Not invasive Nijssen and Groot, 1974
NorwayPresentNative Not invasive Gerstmeier and Romig, 1998
PolandPresentNativeMuus and Dahlström, 1968
RomaniaPresentNative Not invasive Muus and Dahlström, 1968
Russian FederationPresentNative Not invasive Reshetnikov et al., 1997
SerbiaPresentNative Not invasive Gerstmeier and Romig, 1998
SlovakiaPresentNative Not invasive Muus and Dahlström, 1968
SwedenPresentNativeFroese and Pauly, 2008
SwitzerlandPresentNative Not invasive Muus and Dahlström, 1968
UKPresentWheeler, 1992; Winfield et al., 1998Native & non-invasive in southern UK, exotic & invasive in northern UK
UkrainePresentNative Not invasive Shcherbukha Ya, 1982
Yugoslavia (former)Native Not invasive Gerstmeier and Romig, 1998

History of Introduction and Spread

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The introduction of G. cernuus outside their native range has been accidental. The mechanism of introduction is unknown in many cases; however, introductions into England, Wales and Scotland are thought to be from their use as live bait for northern pike (Esox lucius) fishing (Maitland and East, 1989; Winfield, 1992). The transoceanic introduction of G. cernuus into the North American Great Lakes is thought to be via the ballast water of ships (Simon and Vondruska, 1991). DNA analysis shows that the G. cernuus population in the Great Lakes originated from a single founding population source from the Elbe River drainage, Germany (Stepien et al., 2002). Since their discovery in western Lake Superior in 1987, G. cernuus has spread, most likely unaided, approximately 400 miles along the shore by colonizing tributary after tributary (Slade et al., 1994). They have also spread to other areas of Lake Superior (Thunder Bay, ON, Canada) and to Lakes Michigan and Huron (Kindt et al., 1996), most likely in the ballast water of ships.


Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
France 1980s/1990s Yes Ogle (1998) Camargue region. Accidental
Germany 1987 Yes Rösch and Schmid (1996); Winfield et al. (1998) Accidental. Lake Constance
Italy 1980s/1990s Yes Simon and Vondruska (1991) Accidental
Norway 1990s Yes Käläs (1995) Accidental
UK UK 1800s Fisheries (pathway cause) Yes Maitland (1972) Live bait for fishing. Accidental. From Southern England to Wales
UK UK 1980s Yes Maitland and East (1989) Live bait for fishing. Accidental. From Southern England to Loch Lomond, Scotland
UK UK 1980s Yes Winfield (1992) Live bait for fishing. Accidental. From Southern England to Lake Bassenthwaite, Cumbria, England
USA Germany Early 1980s Yes Gunderson et al. (1998); Pratt et al. (1992); Stepien et al. (2002) Ballast water, Elbe River. Accidental. Introduced to Michigan, Minnesota, Wisconsin, USA and Ontario, Canada

Risk of Introduction

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This fish is not considered desirable anywhere within its range; therefore, its intentional introduction is unlikely. Spread from its native range in Eurasia to North America was likely in ballast water. Risk of moving G. cernuus to other fresh or brackish water ports seems possible until effective ballast water treatment is universally initiated. Brown et al. (1998) found that pelagic larval G. cernuus were captured for 8 weeks in the St. Louis River (a tributary and commercial port on Lake Superior), which they suggested increased the risk of being entrained in the ballast water of ships. Spread to new water bodies through connecting channels or accidental introduction is also possible. The movement of G. cernuus from its current limited distribution in Lakes Superior, Michigan and Huron into Lakes Erie and Ontario and eventually into the brackish waters of the Gulf of the St. Lawrence is possible because of connecting channels. They can move slowly on their own or they can be moved in the ballast of ships, although the movement of ballast in the Great Lakes is primarily east to west. If they reach southern Lake Michigan they could pass through a man-made diversion that flows from Lake Michigan into the Illinois River and ultimately into the Mississippi River. If they reach the Mississippi River they will have access to all the major rivers of the central USA. There is a demonstration electrical invasive species barrier that has been operational since 2002 and a new permanent electrical barrier will be constructed in 2008 on the Chicago Sanitary and Ship Canal, which is the connecting channel between the two basins. Operation of this barrier is expected to prevent the spread of Great Lakes invasive species such as G. cernuus into the Mississippi River Basin as long as it remains continuously operational. There is also a risk of spreading G. cernuus with baitfish harvested from the Great Lakes or their tributaries. Baitfish harvest has been restricted in many (but not all) areas where G. cernuus are found in the Great Lakes. The recent discovery of viral hemorrhagic septicaemia virus (VHSV) in the Great Lakes (Elsayed et al., 2006; USDA, 2006; Wren and Lee, 2006) has resulted in more restrictive regulations related to the harvest and distribution of baitfish to prevent the spread of the virus. These regulations, which greatly restrict the movement of baitfish harvested in the Great Lakes to other areas, may also help reduce the risk of spreading G. cernuus as a hitchhiker in live bait. In Europe and Asia, the risk of G. cernuus spreading to un-infested waters is likely to be highest through release by anglers using it as live bait.


Habitat

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G. cernuus tolerate a wide range of habitats. In their native range they are found from near the Arctic Circle south to the Black and Caspian Seas (Popova et al., 1998). They are found in oligotrophic and eutrophic waters, lentic and lotic systems, and brackish water of salinities to 10-12 ppt. They can be in shallow water or at depths to 85 m. Even though habitat can vary considerably, Ogle (1998) made the following three observations regarding habitat preference of G. cernuus: 1) they prefer areas of slow moving water with soft bottoms that are devoid of vegetation; 2) they are associated with the bottom; and 3) they increase in abundance with increasing eutrophication. They also do well in turbid or dark water due to an extremely sensitive cephalic lateral line system and retinal tapetum lucidum (Janssen, 1997; Hölker and Thiel, 1998; Ogle, 1998), which allows them to feed and avoid predators.


Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Brackish
Inland saline areas Secondary/tolerated habitat Natural
Estuaries Principal habitat Natural
Lagoons Secondary/tolerated habitat Natural
Freshwater
 
Lakes Principal habitat Natural
Reservoirs Principal habitat Natural
Rivers / streams Principal habitat Natural
Ponds Secondary/tolerated habitat Natural
Marine
Inshore marine Secondary/tolerated habitat Natural

Biology and Ecology

Top of page Genetics


G. cernuus
appears to be of Paleo-Danube origin and the basal Gymnocephalus species (Ogle, 1998). Stepien et al. (1998) examined the entire mitochondrial DNA control region of G. cernuus and identified five Eurasian haplotypes, which they divided into two groups. One was the eastern group that included the Baltic Sea and Ob’ River, Siberia populations. The other was the western group that included the Danube River and introduced Bassenthwaite Lake, UK populations. They found low intra-population genetic variability in Eurasian G. cernuus, which they attributed to rapid expansion and founder events during post-pleistocene recolonization.

Reproductive Biology

 

While G. cernuus can mature at age one, maturity is more common at age two or three and lengths of 11 to 12 cm. They spawn intermittently and can produce two or more batches of eggs. Following their first spawning, which usually occurs in April or May at water temperatures of 6-20°C (Kovac, 1998; Ogle, 1998), they can spawn again as a second batch of eggs matures typically within 30 days of first spawning. As described in Ogle (1998), the ovaries contain three types of eggs: 1) small, hyaline and colourless; 2) larger opaque, white or pale-yellow to yellow/orange; and 3) large, partially hyaline and yellow/orange. Only types two and three are released during a spawning season. Kovac (1998) reported that four egg size groups have been found and suggested that the number of spawning batches is probably higher than the number of egg size groups. In contrast, Brown et al. (1998) studying the early life history of G. cernuus in the St. Louis River, a tributary to Lake Superior, concluded that G. cernuus spawned over a prolonged period, but that females did not release multiple clutches of eggs. They speculated that water temperatures in the St. Louis River rise and stabilize too quickly for this to occur. G. cernuus are non-guarding spawners that deposit adhesive eggs on plants, logs, branches, sand, clay, gravel, or rocks at depths of 3 m or less (Ogle, 1998). The females generally have 305 to 1540 eggs per g body weight (Kovac, 1998). During first spawning, the females can release 4000 to 200,000 eggs and during a second spawn they can release 352 to 6012 eggs (Ogle, 1998). The eggs are 0.34- 1.3 mm and hatch in 5 -12 days at 10 to 15°C. The embryos are 3.3- 4.4 mm at hatching (Kovac, 1998; Ogle, 1998). The embryos remain sedentary on the bottom for 3-7 days before reaching a size of 4.5-5.0 mm and transitioning to exogenous food. Embryo and larval survival is poor at temperatures below 10°C. The optimal temperature for early development is 15°C (Ogle,1998), for larval development it is 25 to 30°C (Hokanson, 1977), and for age 0 growth it is 21°C (Edsall et al., 1993).

Nutrition


The diet of adult G. cernuus in its native range consists largely of chironomid larvae (Diptera) and macrocrustaceans such as mayflies (Ephemeroptera), caddisflies (Trichoptera), and leeches (Hirudinea) (Adams and Maitland, 1998; Hölker and Thiel, 1998; Kovac, 1998; Ogle, 1998; Popova et al., 1998). When present, G. cernuus will also feed heavily on Pallasea quadrispinosa, Monoporeia affinis, Mysis relicta, Neomysis integer, Gammarus spp., and Diporeia spp. (Hölker and Thiel, 1998; Ogle, 1998). G. cernuus are also known to feed on small fish (Hölker and Thiel, 1998; Popova et al., 1998). The consumption of fish eggs by G. cernuus has been reported in many studies (Adams and Tippet, 1991; Adams and Maitland, 1998; Ogle, 1998; Hölker and Thiel, 1998; Selgeby, 1998), but several other studies suggest that egg consumption is low or non-existent (Ogle et al., 1995; Kovac, 1998; Ogle,1998). Rotifers and copepod nauplii are the first food of G. cernuus. After reaching 1 cm total length they switch to larger cyclopoid copepods, cladocera, and chironomid larvae (Ogle et al., 1995; Ogle, 1998; Popova et al., 1998).

Associations


Throughout its native range G. cernuus are found associated with perch (Perca fluviatilis), northern pike (Esox lucius), roach (Rutilus rutilus), burbot (Lota lota), whitefish (Coregonus lavaretus), and vendace (Coregonus albula), (Lappalainen and Kjellman, 1998; Winfield et al., 1998). Fish associations in a Lake Superior coastal wetland are described by Brazner et al. (1998).

Environmental Requirements


Environmental requirements of G. cernuus are broad. G. cernuus tolerate a wide variety of salinities (10 to 12 ppt), water temperatures, dissolved oxygen concentrations, substrates, depths (to 85 m), lentic and lotic environments, eutrophic to oligotrophic conditions (Adams and Maitland, 1998; Hölker and Thiel, 1998; Kovac, 1998; Lehtonen et al., 1998; Ogle, 1998; Popova et al., 1998). Abundance of G. cernuus generally increases with increasing eutrophication until hypereutrophy is reached (Ogle, 1998). Even though habitat can vary considerably, Ogle (1998) made the following three observations regarding the habitat of G. cernuus: 1) they prefer areas of slow moving water with soft bottoms that are devoid of vegetation; 2) they are associated with the bottom; and 3) they increase in abundance with increasing eutrophication. They also do well in turbid or dark water due to an extremely sensitive cephalic lateral line system and retinal tapetum lucidum (Janssen, 1997; Hölker and Thiel, 1998; Ogle, 1998), which allows them to feed and avoid predators.

Climate

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ClimateStatusDescriptionRemark
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
D - Continental/Microthermal climate Preferred Continental/Microthermal climate (Average temp. of coldest month < 0°C, mean warmest month > 10°C)
Df - Continental climate, wet all year Preferred Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)
Ds - Continental climate with dry summer Preferred Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Preferred Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
67-46

Water Tolerances

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ParameterMinimum ValueMaximum ValueTypical ValueStatusLife StageNotes
Conductivity (µmhos/cm) Optimum Broad tolerance
Depth (m b.s.l.) 10 Optimum 0.25-85 tolerated
Dissolved oxygen (mg/l) 5 6 Optimum 2 tolerated
Hardness (mg/l of Calcium Carbonate) Optimum Broad tolerance
Salinity (part per thousand) 1 Optimum 10-12 tolerated
Turbidity (JTU turbidity) Optimum Broad tolerance
Velocity (cm/h) Optimum Slow moving water
Water pH (pH) 7.0 7.5 Optimum
Water temperature (ºC temperature) 25 30 Optimum 10-30 tolerated. Upper lethal for larvae 30-34

Notes on Natural Enemies

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The primary predators of G. cernuus in Eurasia are the pikeperch (Sander lucioperca) and the northern pike (Esox lucius); other predators include eel (Anguilla anguilla), burbot (Lota lota), white bream (Blicca bjoerkna), and Eurasian perch (Perca fluviatilis) (Eklov and Hamrin, 1989; Adams, 1991; Kovac, 1998; Ogle, 1998). North American species that prey on G. cernuus include northern pike, burbot, lake trout (Salvelinus nanaycush), smallmouth bass (Micropterus dolomieu), black crappie (Promoxis nigromaculatus), bullheads (Ictalurus spp.), walleye (Sander vitreum), and yellow perch (Perca flavescens) (Ogle et al., 1996; Ogle, 1998). Cormorants (Phalacrocorax carbo), kingfishers (Alcedo atthis), and smew (Mergus albellus) are also known to prey on them. Ogle (1992) listed 63 parasites of G. cernuus. No pathological effects were noted for most of those parasites; however, two flukes (Tetracotyle and Cotylurus) appear to have caused significant die-offs (Pokrovskii, 1961; Johnsen, 1965; Swennen et al., 1979) as reported in Ogle (1998).


Means of Movement and Dispersal

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Accidental Introduction


Accidental introduction of G. cernuus has occurred when they have been used live as fishing bait in waters where they are not native (Maitland, 1972; Maitland and East, 1989; Winfield, 1992). Accidental introductions have also occurred via their transport in the ballast water of ships (Pratt et al., 1992; Gunderson et al., 1998; Stepien, 2002).

Intentional Introduction


There are no recorded cases of the intentional introduction of G. cernuus.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Hunting, angling, sport or racingUK - transfer as live bait Yes Maitland, 1972; Maitland and East, 1989; Winfield, 1992
Interconnected waterways Yes

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Baitruffe used as bait in the UK Yes Maitland, 1972; Maitland and East, 1989; Winfield, 1992
Ship ballast water and sedimentUSA and Canada Yes Pratt et al., 1992

Impact Summary

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CategoryImpact
Economic/livelihood Negative
Environment (generally) Negative

Economic Impact

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Leigh (1998) assessed the potential economic impact of the introduction of G. cernuus into the North American Great Lakes and the cost/benefits of a G. cernuus control programme. The underlying assumptions regarding the reductions of Great Lakes species that his economic assessment is based upon were speculative. Ten years after the economic assessment, G. Cernuus have spread to two other Great Lakes, but they have not become abundant outside the St. Louis River and no significant declines in economically valuable native species have yet occurred. However, Leigh’s (1998) analysis demonstrates the potential economic impact of valuable fish species reductions. Leigh analyzed three scenarios. Under the ‘minimum impact’ scenario (a projected decrease of 10% in yellow perch and a 1% decrease in both walleye (Sander vitreum) and whitefish (Coregonus clupeaformis), annual reductions in the commercial and recreational fishery benefits reached nearly US $24 million. Annual projected ‘moderate’ and ‘maximum’ reductions resulted in nearly US $120 and US $215 million reductions in fishery benefits (Leigh, 1998).



Environmental Impact

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G. cernuus have been implicated in population declines of native fish by egg predation (Adams and Tippet, 1991) and competition for food (Kozlova and Panasenko, 1977; Mattila and Bonsdorf, 1989; Bergman, 1991) in some European waters where they have been introduced. While it is not always possible to extrapolate negative interactions documented in laboratory studies to impacts in the wild, several studies conducted in mesocosms or in the laboratory suggest that G. cernuus will out-compete native yellow perch (Perca fluvescens) (Fullerton et al., 1998; Schuldt et al., 1999; Fullerton et al., 2000; Henson and Newman, 2000). However, one laboratory study suggested that if G. cernuus and yellow perch share a habitat, competition for space will be weak or absent and competition for food may occur when food is limiting because neither species has a clear advantage in its ability to consume invertebrates in any habitat (Fullerton and Lamberti, 2006). The general conclusion from the International Symposium on the Biology and Management of Ruffe is that the invasion of G. cernuus to new waterbodies may not be as great a threat to yellow perch, walleye (Sander vitreum), Coregonus spp., and other native fish as was first thought (Adams and Maitland, 1998; Gunderson et al., 1998; Kovac, 1998; Ogle, 1998; Popova et al., 1998; Winfield et al., 1998).

Impact on Biodiversity


There is no evidence that G. cernuus has had a negative impact on biodiversity.

Social Impact

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No precise information is available on the negative social impacts of G. cernuus, but there may be impacts from interference with recreational fishing and bait stealing.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Capable of securing and ingesting a wide range of food
  • Highly mobile locally
  • Fast growing
  • Has high reproductive potential
  • Gregarious
  • Has high genetic variability
Impact outcomes
  • Conflict
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Negatively impacts aquaculture/fisheries
  • Reduced native biodiversity
Impact mechanisms
  • Competition
  • Predation
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult/costly to control

Uses

Top of page Economic Value

There is no reported economic value of G. cernuus.

Social Benefit


There is no reported social value of G. cernuus.

Environmental Services


There are no reported environmental services of G. cernuus.

Uses List

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Animal feed, fodder, forage

  • Bait/attractant
  • Fishmeal

Similarities to Other Species/Conditions

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G. cernuus are similar in appearance to the three other species in its genus – Gymnocephalusbaloni, Gymnocephalus schraestser and Gymnocephalus acerina. Morphological and genetic differences between G. baloni, G. schraestser and G. cernuus are described by Stepien et al. (1998). G. cernuus are also similar in appearance to native North American species. In ‘A Field Guide to Fish Invaders of the Great Lakes Region’, Anderson et al. (2007) provided distinguishing characteristics to differentiate G. cernuus from sauger (Sander canadense), walleye (Sander vitreus), trout perch (Percopsis omniscomaycus), log perch (Percina caprodes) and yellow perch (Perca flavescens).



Prevention and Control

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Since G. cernuus were introduced into the North American Great Lakes, most likely in the ballast water of trans-oceanic vessels, regulations have been enacted to reduce the risk of similar introductions. The Non-indigenous Aquatic Nuisance Prevention and Control Act of 1990 (P.L. 101-646) required that all vessels entering Great Lakes ports from beyond the exclusive economic zone undergo ballast water exchange or some comparably effective ballast treatment that conforms to discharge requirements of the Federal Water Pollution Control Act. These requirements were extended to vessels arriving in ports of the upper Hudson River in 1992. Ships that declare they have no ballast water on board still carry residual water and sediment that could carry live organisms. They were not required to treat their ballast tanks until 2006 when Canada required all vessels that declared they had no ballast on board to conduct saltwater flushing of their ballast tanks before entering the Great Lakes. The USA implemented the same requirement in 2008. These regulations should greatly reduce the risk of additional overseas introductions of G. cernuus into the Great Lakes. 

Public awareness
 

Several public awareness campaigns and educational materials have been developed to teach boaters and anglers about the threats posed by G. cernuus and how to prevent their spread in the USA and Canada. The following web links are examples:

 








Eradication


There have been no attempts to eradicate.

Containment/zoning

 

Baitfish harvesters have been restricted from harvesting bait minnows from Minnesota, Wisconsin and Michigan waters of Lake Superior (Ruffe Control Committee, 1999) to prevent the accidental movement of G. cernuus to un-infested waters with the live bait. However, similar wild baitfish harvest restrictions have not been imposed in all areas of the Great Lakes where G. cernuus are found.

Control  

Physical/mechanical control

 

Intense trawling for G. cernuus in Lake Vortsjarv did not decrease their numbers (Pihu, 1982; Pihu and Maemets, 1982).

Movement control


The US Army Corps of Engineers constructed the temporary electronic dispersal barrier on the Chicago Sanitary and Ship Canal near Romeoville, Illinois, USA. It was activated in April 2002. The electrical fish barrier was built as a demonstration project to study the effectiveness of preventing species migration between the Illinois River and Lake Michigan. A second, more permanent barrier will be constructed in 2008. The new barrier stretches two rows of electrodes across the canal approximately 220 feet apart. The electrodes pulse direct current into the water, causing the fish to turn back rather than pass through the electric current. The electric current poses no threat to people. While constructed to prevent the movement of Asian carp into Lake Michigan, it may also eventually help prevent the spread of G. cernuus out of Lake Michigan into the Illinois and Mississippi Rivers. G. cernuus have been found in Lake Michigan, but as of 2008 were still over 260 miles away from the Chicago Sanitary and Ship Canal.

Biological control


Top down predator control of G. cernuus was attempted in the St. Louis River, a tributary of Lake Superior. Initially walleye and northern pike consumed very little G. cernuus (Ogle et al., 1996). As predators became familiar with G. cernuus as prey they fed more heavily on them. However, researchers concluded that even though predators consumed as much as 47% of the biomass of G. cernuus in one year, they were not able to stop the increase in abundance (Mayo, 1997; Mayo et al., 1998). They further concluded that this attempt at control was unsuccessful, because predators selected native species and avoided G. cernuus. They also suggested that predators never achieved the desired increase in abundance, probably because the St. Louis River is open to Lake Superior, which allowed them to disperse. These results are similar to an experience in the Netherlands where pikeperch populations average size increased when a gillnet fishery was terminated, yet there was no change in G. cernuus catches (Lammens et al., 1990). Increased predators offered some measure of control; however, in a Russian lake (Popova et al., 1998), and the stocking of elvers and enhancing pikeperch and eel populations through protective regulations, resulted in a 5- 7-fold decline in G. cernuus catches in an Estonian lake (Pihu, 1982; Pihu and Maemets, 1982). The use of an alarm pheromone has potential to exclude G. cernuus from particular locations (e.g. spawning areas, entrances to other waterbodies, or ballast tanks) (Maniak et al., 2000) and the use of a sex pheromone has the potential to assist in attracting and trapping G. cernuus or for use in other integrated pest management programmes (Sorenson and Stacey, 2004).

Chemical control


Sensitivity of G. cernuus to various piscicides has been documented, but the effectiveness of the piscicides depends on the fish’s ability to detect and avoid the chemicals. Dawson et al.,(1998) found that lethal concentrations of most formulations, including the most selective toxicant TFM, tended to repel G. cernuus. Antimycin and niclosamide (the active ingredient in bayluscide) did not repel G. cernuus, but delayed-release and sinking formulations (antimycin and bayluscide granules) caused increased swimming and surfacing. They concluded that additional studies are needed before delayed-release formulations of antimycin and bayluscide could be recommended for treating localized populations of G. cernuus.

Control by utilization


G. cernuus
are not generally considered desirable as food anywhere in its range. It is occasionally harvested for use as fishing bait, but there is no harvest significant enough to offer any control. Even intense harvest is unlikely to control their numbers because they are able to compensate for high mortality rates by growing faster, maturing earlier, and spawning more often per season and would likely quickly rebound (Ogle, 1998).

Monitoring and Surveillance


In 1992, the U.S. Fish and Wildlife Service (FWS) initiated a surveillance project in western Lake Superior (Slade and Kindt, 1992), which was expanded in subsequent years to include all the Great Lakes. Ontario Ministry of Natural Resources has conducted surveillance in Canadian waters of the Great Lakes. G. cernuus surveillance in the Great Lakes by all agencies has been reported jointly since 1993 (Slade et al., 1994; Slade et al., 1995; Kindt et al., 1996).  

Gaps in Knowledge/Research Needs

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Some work on the use of piscicides to control G. cernuus has been conducted, but more research on integrated methods to eradicate G. cernuus early in a new invasion are needed.

References

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Links to Websites

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IUCN Red Listhttp://www.redlist.org
Sea Grant National Aquatic Nuisance Species Clearinghousehttp://aquaticinvaders.org
Sea Grant Nonindigenous Species Sitehttp://sgnis.org
United States Geological Surveyhttp://nas.er.usgs.gov

Contributors

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12/04/08 Original text by:

Jeffrey Gunderson, Minnesota Sea Grant College, 2305 E. 5th Street, Duluth, MN 55812, USA

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