BioEd Online

A chemical cocktail that can lure lampreys up streams to spawn has been identified by researchers, who have also managed to synthesize one of the key ingredients. The implications for fisheries management, they say, are vast.

Lampreys are strange creatures, which, despite having no jaws, can parasitically attach themselves to other fish with a toothed disk, and suck out the prey's bodily fluids. Atlantic lampreys (Petromyzon marinus) made their way into the Great Lakes of North America a hundred years ago, and since then have become a massive problem; each lamprey can kill up to 40 pounds of fish that might otherwise have gone to the marketplace.

Now ecologist Peter Sorensen and chemist Thomas Hoye at the University of Minnesota, and their colleagues, say they may have found a way to defeat these lampreys. The key, they say, is the chemicals that lampreys use to find spawning grounds.

The team set out to isolate these compounds from thousands of litres of water containing lamprey larvae, collected from a lamprey farm where 50,000 of the fish are fed and tended for research.

When adult lampreys are ready to breed, they follow the subtle perfume exuded by larval lampreys to find a stream that will be hospitable to their offspring. The team tested the ingredients of the larvae extract to see which one was the best lure.

Shark bait

They found that the most active compound in the mix is a scent closely related to squalamine, a compound so far only found in sharks, where it is thought to act as an antibiotic.

Even tiny concentrations, a single milligram in five Olympic swimming pools of water, are enough to make lampreys follow the scent, the team found.

The researchers have now managed to synthesize the main compound and are working on scaling up its production to levels where it could be used as part of an aggressive programme to stamp out the invaders, they report in Nature Chemical Biology¹.

The approach could also be tried with other fish, says Sorensen; many invasive species use pheremones to navigate.

Fisheries biologist Michael Twohey, of the US Fish and Wildlife Service in Marquette, Michigan, is helping put the research into action. "We're very excited about it. It holds the promise to implement another strategy for controlling sea lampreys." Twohey says that the Great Lakes Fisheries Commission plans to be using it on a wide scale by 2010.

Lamprey support

Fish pheromones could be used in conservation efforts as well, says Sorensen. Populations of Pacific lampreys, which spend their larval stage in rivers in the Pacific Northwest, are in dangerous decline. Artificial pheromones could be used to help adults find their way back to streams, even if no larvae have survived to attract them to suitable breeding grounds.

Lampreys are important to the tribes of Native Americans living besides the rivers in the area, both as food and as an object of cultural significance, notes David Close, a research scientist with the Confederated Tribes of the Umatilla Indian Reservation in Pendlton, Oregon. "Lampreys are not as glamorous as salmon, so society doesn't pay very much attention," he adds.

"There are myths and legends associated with the life history of the lamprey. We're losing not just a food item but a part of our culture," says Close, who says the new work is "very encouraging and very exciting".