Sea lampreys feed off the blood of large fish, including trout, salmon, whitefish, carp, catfish and sturgeon. The sea lamprey is native to the Atlantic Ocean but infiltrated the Great Lakes region in the 1920s and '30s during canal construction.
The sea lamprey resembles an eel and feeds off of larger fish by attaching itself to the side of the fish. The sea lamprey then consumes the blood and fluids that come through the wound. A secreted enzyme prevents the fish's blood from clotting, allowing the sea lamprey to eat for hours, days or weeks.
Most fish can survive a sea lamprey attack but will be left with a circular wound. An attacked fish may suffer from decreased weight and, in severe cases, succumb to an infection in the wound and die.