Unlike most fish, a lamprey's body has cartilage but no bones, scaleless skin, no paired fins, no lateral line, and no swim bladder. Sea lampreys entered the Great Lakes from the Atlantic Ocean through man-made shipping canals and were first observed in Lake Ontario in the 1830's. Niagara Falls acted as a natural barrier preventing sea lamprey movement to Lakes Erie, Huron, Michigan, and Superior. However, when the Welland Canal, constructed to bypass the falls, was deepened in 1919, sea lampreys gained access to the rest of the Great Lakes. By 1938, they had invaded all of the Great Lakes.
Sea lampreys are parasitic pests.
They attach to fish with their suction mouth and teeth, and use their tongue to rasp through a fish's scales and skin so they can feed on its blood and body fluids. A single sea lamprey will destroy up to 40 lbs. Sea lampreys are so destructive that, under some conditions, only one out of seven fish attacked will survive. In the 1940's and 1950's, sea lamprey populations exploded as there were no effective control methods. This contributed significantly to the collapse of fish species that were the economic mainstay of a vibrant Great Lakes fishery.