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Short Features

Illustration by Jack Molloy
Illustration by Jack Molloy

Invasion of the Bloodsuckers

Will biotechnology control lampreys in the Great Lakes?

It's a cool day in May, and Stacia Sower is standing waist-deep in a containment pool at the top of a fish ladder on the Cocheco River in Dover, N.H. She strains to lift a net full of writhing sea lampreys out of the pool and carries it to her nearby truck, where she dumps them into a tank. Over the next few days, she will collect up to 200 of the eel-like parasites and take them to the Anadromous Fish Laboratory at the University of New Hampshire, where they will finish their spawning run in an artificial stream within a 17-foot-long tank.

Sower, a professor of biochemistry and molecular biology, has been studying the behavior of spawning sea lampreys for more than 20 years, searching for a safe and effective way to control their population. These primitive, scaleless fish begin life as toothless larvae, feeding on microorganisms in the mud of freshwater streams and lakes. After several years, they transform into rusty-brown adults. Then they move into the sea to begin a parasitic life, attaching to fish by their round, sucker-like mouths and feeding on the blood and tissues of the hosts. This stage lasts about 15 months, after which the adult lampreys, now up to three feet long, return to fresh water to spawn and die.

Stacia Sower
Professor Stacia Sower

Lampreys are not a problem in New Hampshire waters. In fact, the filter-feeding larvae benefit the environment by helping to keep streams clean. But in the Great Lakes, it's a different story.

There were no sea lampreys in the Great Lakes until 1829, when the Welland Canal bypassed the natural barrier of Niagara Falls and opened a route to the lakes from the Atlantic Ocean. Once they reached the lakes, the lampreys adapted so they could spend their entire lives in fresh water. By the 1940s, they were taking a heavy toll on lake trout and other commercially valuable fish, compounding problems caused by pollution and overfishing.

Today, sport fishing in the Great Lakes is a multibillion-dollar industry, thanks to cleaner water and a successful two-part approach to lamprey control. Fisheries biologists have developed an effective chemical treatment to kill lamprey larvae in the small rivers and streams that feed the lakes, but it doesn't work in bigger waterways. There they try to reduce the successful spawn by catching male lampreys, sterilizing them and returning them to the rivers to compete for mates.

The problem with this approach, Sower explains, is that the chemical used to sterilize the lampreys is expensive, extremely hazardous to humans and persistent in the treated lampreys. It is so toxic that there is only one place where it can be used: a special facility built for that purpose at a biological research center in Michigan. All of the lampreys to be treated have to be trucked to that facility, injected with the chemical and then returned to the rivers where they were caught.

Sower believes that bioengineering can provide a better solution. "I started in 1980 looking at whether you could control reproductive behavior through the brain," she explains. "Most people didn't think so, because lampreys are so primitive. But since they are seasonal and respond to environmental factors, I thought we could probably find some kind of brain control."

Fish and lamprey eel

Indeed, Sower has found a reproductive hormone that can be altered to sterilize male lampreys without affecting their sexual behavior. "Substituting the right amino acid in this hormone will produce an animal with no viable sperm. Those males will continue normal reproductive behavior, however, so females won't reject them," she says.

The hormone in question is a protein made up of ten amino acids. Sower is designing an analog in which one amino acid will be changed. Much of her research has been devoted to finding the right amino acid through trial and error, a process complicated by the fact that tests can be conducted only once a year, when the lampreys are spawning.

The synthetic hormone that Sower is developing will be inexpensive to produce and harmless to humans and the environment. Biologists will be able to inject lampreys right at the fish ladders where they are collected and then return them to the water immediately. Even fish or animals that eat the lampreys after they spawn will be in no danger, because the synthetic hormone degrades rapidly, breaking down in the lamprey's body within a matter of hours.

"It has been a long process, but we are getting close," Sower says. "We hope to have our synthetic hormone approved by the Food and Drug Administration and available for use within five years."

--Bill Burtis

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