Eurasian ruffe, Pope
The ruffe (Gymnocephalus cernua), also known as the Eurasian ruffe or pope, 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, 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 Gymnocephalus, which as a whole is native 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 can reach up to 25 cm (9.8 in) 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 which is 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.
The species occurs in the basins of the Caspian, Black, Aral, Baltic and North Sea, and is also found in Great Britain, parts of Scandinavia and some regions of the Arctic Ocean basin eastward to the drainage of the Kolyma. It has been introduced to parts of Western Europe (France, northern Italy) and Greece, as well as to the North American Great Lakes.
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 learn, it has kept the same diet in its transfer to the Great Lakes.
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 (0.013 to 0.051 in) 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 (0.014 to 0.019 in), while the first batch of eggs goes from 0.90 to 1.213 mm (0.0354 to 0.0478 in) 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 10–15 °C (50–59 °F).The next stage in life is the embryonic/juvenile stage. Embryos that are freshly hatched are between 3.5 and 4.4 mm (0.14 and 0.17 in) in size. These embryos are sedentary for 3–7 days, and in that time grow to about 4.5 to 5.0 mm (0.18 to 0.20 in) 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 20 cm (7.9 in), and a maximum of 29 cm (11 in) 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.
