The Eurasian Ruffe (Gymnocephalus cernuus)'s a freshwater fish found in temperate regions of Europe and northern Asia. It's been introduced into the Great Lakes of North America, reportedly with unfortunate results. Description 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's usually 4-6 inches in length and will never exceed 10 inches, but's a very aggressive fi… (More on Ruffe)