It prefers the darkness and has a large spiny dorsal fin which is unpalatable to predators. Large sensory organs can detect prey and predators. They live in shoals in still waters and slow running rivers.
The ruffe's colors and markings are 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 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.