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Two sea lampreys attached to a pane of glass

Not especially pretty Lampreys seal their round mouths onto a prey fish by suction and use sharp teeth to rasp out a hole from which to suck the victim's body juices.

Putting lampreys on the lam

Researchers find chemical that lures lampreys to spawning grounds

By Deane Morrison

From M, winter 2006

Any way you slice it, the sea lamprey is a slippery customer. Sinuous as an eel, the lamprey invaded the Great Lakes early in the 20th century and soon laid waste to stocks of lake trout, whitefish, and other commercially valuable species. The scope of the problem is immense: Last year the U.S. and Canadian governments poured more than $16 million into lamprey control. The major means has been a poison that kills lamprey larvae but plenty of innocent species, too. The Great Lakes Fishery Commission (GLFC), whose job is to control lamprey, has set a goal of finding a new control measure by 2010. Enter Peter Sorensen. About 16 years ago the professor of fisheries, wildlife, and conservation biology set out to find a natural chemical to control the scourge of the Great Lakes. He pitted himself against a foe that spends most of its life hidden in streambeds as a small, sliver-shaped larva and only about a year as an adult plying the lakes before finding streams for spawning. This year he succeeded. Sorensen, along with chemistry professor Thomas Hoye and their students and colleagues, identified a chemical attractant (pheromone), produced by lampreys themselves, that may be useful in leading the fish to traps.

Sorensen plans to apply what he's learned about fish pheromones to the control of other invasive species, such as the common carp and perhaps the Asian carp.

Even though adult lampreys live only about a year, they kill on average 40 pounds of fish, says Sorensen. And it isn't pretty. Lampreys seal their round mouths onto a prey fish by suction and use sharp teeth to rasp out a hole from which to suck the victim's body juices. As adults near the end of their life spans, they cease feeding and seek out a suitable stream in which to spawn, after which they die. En route to spawning, they follow chemical trails laid down by larval lamprey in streambeds, picking up the scent like aquatic bloodhounds. The first migratory pheromone identified in any fish, it draws the adults so well that extracts of water from larval lamprey nurseries improved adult capture rates sixfold during experiments in Michigan streams. How much better, Sorensen and his colleagues reasoned, if they could use the pure pheromone. To find it, Sorensen and graduate student Jared Fine sifted through 8,000 liters of water from tanks holding 35,000 lamprey larvae. They came up with less than a milligram, or 35 millionths of an ounce, of pheromone. They then sought help from Hoye, who, along with Vadims Dvornikovs, Christopher Jeffrey, and Feng Shao--all researchers in Hoye's lab--identified and synthesized the pheromone. It had three components, the main one a steroid never seen before. "Chemically, it's closest to a shark chemical that is being developed as an anticancer agent," says Sorensen. "And it appears that more than one species of lamprey use this same compound." So potent is the pheromone, lamprey can smell a single gram dissolved in 14 billion liters of water--enough to fill in excess of 5,000 Olympic-sized swimming pools. It will take a few years to scale up production of the pheromone, but when that happens, the researchers foresee several benefits. For one thing, they envision traps baited with the pheromone drawing adult lampreys to a spot where males can be separated and sterilized, then released to spawn. Or, trapped lampreys may be removed to streams unsuited for spawning, where they will die. On the flip side, the pheromone may be used to help replenish stocks of lamprey valued as food by some west coast American Indian tribes and by some Europeans. The pheromone could possibly be used to guide lampreys to good spawning grounds where no larvae are around to do the job. A further use would be to help target lamprey control to streams where the problem is most severe. "By measuring concentrations of the pheromone in water, we may be able to estimate the number of lamprey larvae in the water," says Sorensen. He plans to apply what he's learned about fish pheromones to the control of other invasive fish, such as the common carp and perhaps the Asian carp. Apart from their status as nasty parasites, lampreys hold a certain fascination for the researchers. Lampreys have existed for almost 400 million years, predating the evolution of jaws and bony skeletons. Their cartilage-based skeletons are akin to those of sharks, skates, and rays, so it's hardly surprising that their migratory pheromone should resemble a chemical made by sharks. That chemical, produced by the "dogfish" shark and known as squalamine, has been reported to inhibit the growth of blood vessels that nourish tumors while sparing other blood vessels. In the sharks, it also appears to function as an antibiotic. Therefore, say the researchers, the ancestors of lamprey may have simply "borrowed" a compound used to fight infections and adapted it as an attractant. The work is the cover story for the November issue of Nature Chemical Biology.