Easily identified by its underside suction disk that has a clam shell-like appearance, which helped anglers catch 120 of them in and around Lake Superior in 1998. Believed to have been intentionally introduced for aquarium use in the 1960s. Depletes water oxygen levels for wildlife. Great Britain, Northern Europe, Caspian Sea. Entered via ballast water in 1984.
Small crustacean competes with small fish for food and reproduces rapidly.
Sharp spine makes it hard for other fish to swallow.