Compound prevents bloodsuckers from invading the Great Lakes

Authorities declared a rare victory over an invasive blood-sucking fish that nearly collapsed the $7 billion fishing industry in the Great Lakes region. More than a century ago, through human activity, lampreys, native to the Atlantic Ocean, entered the Great Lakes. There, they began devouring local fish, from salmon to lake trout and walleye, according to National Geographic.

“Basically, they just swim in. We opened the door to them when we built the canal,” said Greg McClinchey, director of policy and legal affairs for the Great Lakes Fisheries Commission (GLFC), an international organization international focus on lamprey control, said. “We still don’t fully understand what this species can do.”

A lamprey can kill up to more than 18 kg of fish in the larval stage of its life cycle. Each female lamprey will lay about 100,000 eggs, about 75% of which will survive. According to McClinchey, at their peak, they consumed more than 45 million kilograms of fish, far exceeding humans. They also destroy natural ecosystems more than humans. Not only are fish in the Great Lakes unprepared to defend themselves against lampreys, the region also lacks natural predators that help control the invasive species.

A decades-long campaign to control invasive lampreys has achieved unprecedented success around the world. The secret to success is a new chemical called lampricide that kills about 90 to 95 percent of lampreys in the Great Lakes, but does not harm endemic species. The campaign saved the Great Lakes fishery, according to Marc Gaden, executive secretary of the Great Lakes Fishery Commission.

The mechanism of lamprey hunting is very simple. Without regular teeth, they use sharp weapons called tooth plates. Lampreys use tooth plates to cling to the body of any fish, then punch holes in the prey’s abdominal cavity to create an open wound. Their saliva prevents wounds from healing, allowing them to continuously suck blood. As a result, the host will feel very uncomfortable. When lampreys began their invasion in the mid-20th century, fishermen complained that when they pulled in their nets, they came across so many dead fish that they held their nets tight. Lampreys consume fish five times faster than the rate of commercial fishing.

In 1954, an agreement between the two countries, eight states, one province and several tribes led to the birth of the GFLC. When local authorities tried to control lampreys by using dams, electric shocks and even using giant sieves, but they were ineffective. They need to find a solution that can destroy the larvae in the stream bed before they transform into nearly adult fish, swim into the lake and destroy native fish. That was the origin of the lampricide program.

In 1950, scientists at the University of Michigan began working with authorities at the Hammond Bay Biological Station on the shore of Lake Huron. They looked at a chemical that would kill invasive fish but not affect native species. After seven years of testing, comparing the mortality rates of native fish and lamprey injected with the same compound, researchers discovered 3-trifluoromethyl-4-nitrophenol, or TFM, a compound that invasive fish do not evolve to transform.

TFM quickly became the backbone of GLFC’s control program. Many teams are deployed to spray TFM in shallow streams where lamprey larvae gather before moving to deeper water as adults to hunt. Deep waters remained a haven for lampreys until the use of niclosamide in the 1990s, a poison that sinks to the bottom and targets river bottoms. The current program maintains the same tactics, incorporating the use of dams to limit the spread of lampreys.

After a long interruption due to Covid-19, processing returned to normal in 2022. Lamprey numbers began to gradually decrease. Currently, GLFC kills about 8.5 million lampreys each year. Researchers are also exploring alternatives, including the use of genetic modification and CRISPR.