The Eurasian ruffe (''Gymnocephalus cernua''), also known as ruffe or pope, is a freshwater

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

found in temperate regions of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

and northern

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

. It has been introduced into the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

, reportedly with unfortunate results, as it is invasive and is reproducing faster than other species. Its common names are ambiguous – "ruffe" may refer to any local member of its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

Gymnocephalus ''Gymnocephalus'' is a genus of ray-finned fishes from the family Percidae, which includes the perches, pike-perches and darters. They are from the Western Palearctic area, although one species, ''Gymnocephalus cernua'' has been accidentall ...

'', which as a whole is native to

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelag ...

Description

The ruffe's colors and markings are similar to those of the

walleye The walleye (''Sander vitreus'', synonym ''Stizostedion vitreum''), also called the yellow pike or yellow pickerel, is a freshwater perciform fish native to most of Canada and to the Northern United States. It is a North American close relat ...

, an olive-brown to golden-brown color on its back, paler on the sides with yellowish white undersides. The ruffe can reach up to in length, but is usually around half that size. It is a very aggressive fish for its size. The ruffe also has a large, spiny

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

which is likely distasteful to its

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...

s. It also has two fins on top, the front fin has hard and sharp spines, the back fin has soft spines called rays. The most obvious features to recognize a ruffe are the ruffe's large, continuous dorsal fin and its slightly downturned mouth.

Distribution

The species occurs in the basins of the Caspian,

Black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white ha ...

, Aral,

Baltic Baltic may refer to: Peoples and languages *Baltic languages, a subfamily of Indo-European languages, including Lithuanian, Latvian and extinct Old Prussian *Balts (or Baltic peoples), ethnic groups speaking the Baltic languages and/or originatin ...

and

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian ...

, and is also found in

Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It ...

, parts of

Scandinavia Scandinavia; Sámi languages: /. ( ) is a subregion in Northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. In English usage, ''Scandinavia'' most commonly refers to Denmark, Norway, and S ...

and some regions of the Arctic Ocean basin eastward to the drainage of the

Kolyma Kolyma (russian: Колыма́, ) is a region located in the Russian Far East. It is bounded to the north by the East Siberian Sea and the Arctic Ocean, and by the Sea of Okhotsk to the south. The region gets its name from the Kolyma River ...

. It has been introduced to parts of Western Europe (France, northern Italy) and Greece, as well as to the North American

Diet

In Eurasia, the ruffe diet mainly consists of zoobenthos:

chironomid The Chironomidae (informally known as chironomids, nonbiting midges, or lake flies) comprise a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae. Many specie ...

s, small aquatic bugs and larvae, which are all found in the

benthic zone The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning " ...

of the water column. As far as researchers have been able to learn, it has kept the same diet in its transfer to the Great Lakes.

Reproduction

The ruffe has the capacity to reproduce at an extremely high rate. A ruffe usually matures in two to three years, but a ruffe that lives in warmer waters has the ability to reproduce in the first year of life. A single female has the potential to lay from 130,000 to 200,000 eggs annually. Ruffe will leave the deep dark water where they prefer and journey to warmer shallow water for spawning. The primary

spawning Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquat ...

season for the ruffe occurs from the middle of April through approximately June.

Life cycle

Life for the Eurasian ruffe, starts as an egg, like other fish. Egg sizes typically range from in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid f ...

, depending on the size of the female. If the same female has a second batch in the same season, the eggs will be smaller than the first batch. The size of the second batch of eggs is about , while the first batch of eggs goes from in size. If the female lays twice in one season, there is usually one in late winter/early spring and one in late summer. Hatching occurs in 5–12 days in temperatures of . The next stage in life is the embryonic/juvenile stage.

Embryos An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

that are freshly hatched are between in size. These embryos are sedentary for 3–7 days, and in that time grow to about in length. One week after the hatching, the young ruffe start to swim and feed actively; they do not form schools at this age. From here, the ruffe gradually mature until they are 2–3 years old, when they reach full maturity. At full length, the adult ruffe is usually around , and a maximum of Growth usually occurs more when the ruffe is in clear, brackish waters. Generally, female and male ruffe do not live longer than 7 to 11 years.

Presence in the North American Great Lakes area

Ecological effects

The introduction of the ruffe seems to be causing much damage to

Lake Superior Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh wa ...

. This fish's invasion of the lake has not only caused problems with space, but competing with other fish for food supply. The ruffe has similar eating habits, but an accelerated reproduction rate compared to other similar fish. Therefore, having more ruffe in the water leads to less food for other fish. This fish is unique in its ability to adapt in many

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s and

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

s, resulting in success despite such factors as

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

or other biological changes. The ruffe also has an exceptional ability to detect water vibrations through organs called neuromasts. This trait both aids the ruffe in finding food and gives the ruffe an edge in avoiding predators. These develop into more advanced and sensitive organs as the fish matures; of note, the

perch Perch is a common name for fish of the genus ''Perca'', freshwater gamefish belonging to the family Percidae. The perch, of which three species occur in different geographical areas, lend their name to a large order of vertebrates: the Per ...

's neuromasts weaken as it matures. The ruffe has the potential to overtake many other fish species, and consequently damage the Great Lakes'

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

. Without concerted intervention, the ruffe have the potential to ruin Lake Superior. The ruffe is the first invasive species to have been classified as a nuisance by the Non-indigenous Aquatic Nuisance Prevention and Control Program. Along with it being the most populous fish in the St. Louis river basin, it has disrupted ecosystems all across the Great Lakes. The invasion was first noticed in the 1980s by the DNR. They suggest that the fish was introduced to the lake via ballast water that was dumped into the

Duluth, Minnesota , settlement_type = City , nicknames = Twin Ports (with Superior, Wisconsin, Superior), Zenith City , motto = , image_skyline = , image_caption = Clockwise from top: Downtown Dul ...

, harbor by anchored freight ships. Ever since the ruffe were detected, studies have shown that the ruffe and the

yellow perch The yellow perch (''Perca flavescens''), commonly referred to as perch, striped perch, American perch, American river perch or preacher is a freshwater perciform fish native to much of North America. The yellow perch was described in 1814 by Sam ...

are closely related and are quickly becoming rivals. The ruffe and perch are competing in numbers and are also competing for food; this is a match that the ruffe are winning.

Control

Ever since the ruffe was introduced into the Great Lakes system, scientists and fishery managers have been searching for the right way to get rid of them. In the beginning, the main method of control was to increase the

Walleye The walleye (''Sander vitreus'', synonym ''Stizostedion vitreum''), also called the yellow pike or yellow pickerel, is a freshwater perciform fish native to most of Canada and to the Northern United States. It is a North American close relat ...

and

Northern Pike The northern pike (''Esox lucius'') is a species of carnivorous fish of the genus ''Esox'' (the pikes). They are typical of brackish water, brackish and fresh waters of the Northern Hemisphere (''i.e.'' holarctic in distribution). They are kno ...

populations, because they are natural predators of the ruffe. Other methods that have been considered are poison and chemical control. If a large school of ruffe is found, they can be poisoned. If some survive, however, they will rapidly reproduce. Chemicals can be targeted to act on specific species of fish. The chemical lampricide TFM kills ruffe, but leaves other fish unharmed. As long as a couple of the fish survive, they can move and repopulate. The problem will increase if the ruffe invade southern river systems. The use of

pheromones A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

is being investigated as a control. After extensive studies, scientists discovered that the ruffe can be repelled by their own alarm pheromone. When injured, a ruffe will release this pheromone into the water to warn other ruffe to stay away. Scientists have concluded three things: *The pheromone repels the ruffe (it was unclear if it would in the beginning). *The pheromone is species specific, so it would only repel the ruffe, none of the other fish. *The pheromone is resilient to freezing, so could be used even during Minnesota's long winter season; the ruffe could still be controlled. By using this method, scientists could block ruffe from natural mating spots and produce a population decline; their goal is to kill the species in the Great Lakes.

Other invasive situations

Ruffe were first discovered in

Loch Lomond Loch Lomond (; gd, Loch Laomainn - 'Lake of the Elms'Richens, R. J. (1984) ''Elm'', Cambridge University Press.) is a freshwater Scottish loch which crosses the Highland Boundary Fault, often considered the boundary between the lowlands of ...

, Scotland, in 1982, probably introduced as live bait by pike anglers. It is now abundant throughout the Loch. There are concerns about the effect of the huge ruffe population on the endemic whitefish population known as

powan The powan (''Coregonus clupeoides'') is a kind of freshwater whitefish endemic to two lochs in Scotland, Loch Lomond and Loch Eck.Freyhof, J. & Kottelat, M. (2008''Coregonus clupeoides''.In:IUCN Red List of Threatened Species. Version 2010.1. ( ...

(''

Coregonus lavaretus ''Coregonus lavaretus'' is a species of freshwater whitefish, in the family Salmonidae. It is the type species of its genus '' Coregonus''. There are widely different concepts about the delimitation of the species ''Coregonus lavaretus'' and a ...

'') as ruffe prey on their eggs. Ruffe became the principal food item for the three main fish predators found in the area: the

great cormorant The great cormorant (''Phalacrocorax carbo''), known as the black shag in New Zealand and formerly also known as the great black cormorant across the Northern Hemisphere, the black cormorant in Australia, and the large cormorant in India, is a w ...

grey heron The grey heron (''Ardea cinerea'') is a long-legged wading bird of the heron family, Ardeidae, native throughout temperate Europe and Asia and also parts of Africa. It is resident in much of its range, but some populations from the more north ...

and

northern pike The northern pike (''Esox lucius'') is a species of carnivorous fish of the genus ''Esox'' (the pikes). They are typical of brackish water, brackish and fresh waters of the Northern Hemisphere (''i.e.'' holarctic in distribution). They are kno ...

References

Sources

*Gangl, James Allen. 1998. "Effects of Eurasian Ruffe (''Gymnocephalus cernuus'') and Yellow Perch (''Perca flavescens'')." M.S. Thesis. University of Minnesota, Duluth. Pg. 1–5 *McLean, Mike. "Ruffe: A New Threat to Our Fisheries." Minnesota Sea Grant. 24 July 2007.1 Oct 2007 http://www.seagrant.umn.edu/ais/ruffe_threat * *Crosier, Danielle M., Molloy, Daniel P., Marsden, J. Ellen.
Ruffe – ''Gymnocephalus cernuus''
" New York State Museum. University of Vermont. October 23, 2007.

External links

GLANSIS Species FactSheet

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

Species Profile – Eurasian Ruffe (''Gymnocephalus cernuus'')
National Invasive Species Information Center,

United States National Agricultural Library The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Located ...

. Lists general information and resources for Eurasian Ruffe. {{Taxonbar, from=Q187981 Gymnocephalus Fish described in 1758 Taxa named by Carl Linnaeus Freshwater fish of Europe Fish of Europe Fish of Asia Fish of Russia Fish of the Great Lakes