Gymnocephalus cernuus, Photo: Michael Lahanas
Gymnocephalus cernuus (Linnaeus, 1758)
* Acerina cernua (Linnaeus, 1758)
* Gymnocephalus cernuus Report on ITIS. Retrivied [03-12-2008], from the Integrated Taxonomic Information System (ITIS). 
The Eurasian Ruffe (Gymnocephalus cernuus) or simply Ruffe is a freshwater fish found in temperate regions of Europe and northern Asia. It has been introduced into the Great Lakes of North America, reportedly with unfortunate results. Its common names are ambiguous – "ruffe" may refer to any local member of its genus Gymnocephalus, which as a whole is natively endemic to Eurasia.
The ruffe's colors and markings are similar to those of the walleye, an olive-brown to golden-brown color on its back, paler on the sides with yellowish white undersides. The ruffe is usually 4-6 inches (10 - 25 cm) in length and will never exceed 10 inches, but is a very aggressive fish for its size. The ruffe also has a large, spiny dorsal fin likely distasteful to its predators. 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.
In Eurasia, the ruffe diet mainly consists of zoobenthos: chironomids, small aquatic bugs and larvae, which are all found in the Benthic zone of the water column. As far as researchers have been able to find, it has kept the same diet in its transfer to the Great Lakes.
Ruffe eat the young of the signal crayfish which is threatening many European water creatures.
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 season for the ruffe occurs from the middle of April through approximately June.
Life, for the Eurasian ruffe, starts as an egg, like other fish. Egg sizes typically range from 0.34 to 1.3 mm in diameter, 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 0.36 to 0.47 mm, while the first batch of eggs goes from 0.90 to 1.21 mm 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 ranging from 10 to 15 degrees Celsius. The next stage in life is the embryonic/juvenile stage. Embryos that are freshly hatched are between 3.5 to 4.4 mm in size. These embryos are sedentary for 3–7 days, and in that time grow to about 4.5 to 5 mm in length. One week after the hatching, the young ruffe start to swim and feed actively, but 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 20 cm, but at a maximum of 29 cm. Growth is 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 Great Lakes area
The introduction of the ruffe seems to be causing much damage and has become a big inconvenience to Lake Superior. This pesky fish's invasion on the lake has not only caused problems with space, but problems with food supply to other fish as well. The ruffe has similar eating habits, as well as having an accelerated reproduction rate compared to other like 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 habitats and temperatures, resulting in its way of life can be maintained with little interference from climate change or other biological changes. The ruffe also has an excepional ability to detect water vibrations through organs called neuromasts. This trait both aids the ruffe in finding food and gives the rudge an edge in avoiding predators. These will develop into more advanced and sensitive organs as the fish matures; for example, the perch's neuromasts weaken as it matures. The ruffe has the ability to overtake many other fish species, and consequently damage the Great Lakes ecosystems. If there is no intervention taken by the public the ruffe have the potential to ruin Lake Superior.
Not only has the ruffe become an inconvenience but, it is also the first invasive species to have been labeled a nuisance by the Non-indigenous Aquatic Nuisance Prevention and Control Program. Along with it being the most populated 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 harbor by anchored freight ships. Ever since the ruffe were detected, studies have not only shown that the ruffe and the yellow perch are closely related but they 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. It shouldn't be too long for the ever so quickly reproducing ruffe to soon phase out any perch that stands in its way. Some researches believe that if a plan isn't thought of soon, this fish could be the only kind left in the Great Lakes area.
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 and Northern Pike populations because they are natural predators of the ruffe. Even though this really didn't work in the beginning, it is still too early to tell because it takes a couple years for fish to switch to a new food source.
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 of them survive, however, the problem will only continue. Chemicals, on the other hand, can be specifically made to only harm a certain kind of fish. The chemical lampricide TFM kills ruffe, but leaves other fish untouched.
The major problem with this though, is that as long as a couple of the fish survive, they can move and repopulate. The problem would increase if the ruffe started to move farther down south. A new method of control is being investigated to prevent this: pheromones. After an extensive amount of tests, 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. After doing these tests, the scientists involved concluded three significant things. One, that the pheromone does repel the ruffe (it was unclear if it would in the beginning). Second, the pheromone is species specific, so it would only repel the ruffe, none of the other fish. Finally, the scientists found that it is resilient to freezing, so even during Minnesota's long winter season; the ruffe could still be controlled. By using this method there is a chance the ruffe could be prevented to go to their natural mating spots and therefore eventually the ruffe might die out.
* World Conservation Monitoring Centre (1996). Gymnocephalus cernua. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006.
Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License