- Eurasian ruffe are small members of the European perch family. They were first discovered in Duluth harbor in 1985.
- Ruffe have spread to other rivers and bays around Lakes Superior and have established a population in Thunder Bay near Alpena, Michigan.
- In some areas, ruffe have shown explosive population growth and have displaced valuable native species such as yellow perch as well as emerald shiners and other forage fish. Their sharp spines make them difficult for larger fish to eat.