The sea lamprey—an ancient Atlantic fish that wreaked havoc on the Great Lakes—may be America’s first destructive invasive species.

The rasping mouth of the sea lamprey, an infamous Great Lakes invader.

Among the most primitive of all vertebrate species, the sea lamprey is a parasitic fish native to the northern and western Atlantic Ocean. Due to their similar body shapes, lampreys are sometimes inaccurately called “lamprey eels.”

Unlike “bony” fishes like trout, cod, and herring, lampreys lack scales, fins, and gill covers. Like sharks, their skeletons are made of cartilage. They breathe through a distinctive row of seven pairs of tiny gill openings located behind their mouths and eyes.

But the anatomical trait that makes the sea lamprey an efficient killer of lake trout and other bony fishes is its disc-shaped, suction-cup mouth, ringed with sharp, horny teeth, with which it latches on to an unfortunate fish. The lamprey then uses its rough tongue to rasp away the fish’s flesh so it can feed on its host’s blood and body fluids. One lamprey kills about 40 pounds of fish every year.

Sea lampreys invaded the Great Lakes in the 1830s via the Welland Canal, which connects Lakes Ontario and Erie and forms a key section of the St. Lawrence Seaway. Within a decade, they had gained access to all five Great Lakes, where they quickly set to work predating on the lakes’ commercially important fishes, including trout, whitefish, perch, and sturgeon. Within a century, the trout fishery had collapsed, largely due to the lamprey’s unchecked proliferation.

Today, the Great Lakes Fishery Commission coordinates control of sea lampreys in the lakes, which is conducted by the U.S. Fish and Wildlife Service and Fisheries and Oceans Canada. Field biologists set up barriers and traps in the streams that feed the lakes to prevent the lamprey’s upstream movements, and apply special chemicals, called lampricides, that target lamprey larvae but are harmless to other aquatic creatures.

New techniques to control sea lampreys are always under development. Since sea lampreys use odors, or pheromones, to communicate, scientists have replicated these odors to increase the efficacy of current control methods.