MINNEAPOLIS / ST. PAUL-For the rats of Hamelin, it was the PiedPiper's tune. For the destructive sea lamprey of the Great Lakes, it'sa chemical attractant, or pheromone, released by lamprey larvae livingin streambeds. Following the pheromone trail, adults are drawn tostreams favorable for spawning. Researchers have long wanted toidentify the pheromone so it could be synthesized and used to controlthe sea lamprey, which laid waste to Great Lakes fisheries of laketrout and other species in the mid-20th century. Now, a team ofUniversity of Minnesota researchers has identified the three majorcomponents of the pheromone and synthesized the principal one, a novelsteroid akin to a shark steroid that possesses anticancer activity.This is the first migratory attractant to be identified in any fish.The work is the cover story for the November issue of Nature ChemicalBiology and will be published online in the journal Sunday, Oct. 2.
The lamprey is one of the earliest relics of vertebrate evolution,dating back nearly 400 million years, before the evolution of jaws andbony skeletons. The species parasitizes other fish by attaching withtheir circular, toothy mouths and sucking the body juices. A singlelamprey will feed for about a year, consuming on average 40 pounds offish. In the Great Lakes, their prey have been commercially valuablespecies like lake trout and whitefish.
Currently, the Great Lakes Fishery Commission (GLFC) controls lampreyby means of a poison that kills lamprey larvae in streambeds. It alsokills every invertebrate it comes in contact with, and sometimes fish.The lampricide is tanker-trucked to streams, some of them in populatedareas, in an expensive, labor-intensive and unpopular undertaking. TheGLFC is eager to use a synthetic form of the newly found pheromone toreplace the poison by luring lamprey to traps and sterilizing themales, the researchers said. Using the pheromone would beenvironmentally friendly and less expensive.
"The GLFC has the goal of controlling lamprey with a new and bettertechnique by 2010. This could be it," said Peter Sorensen, a professorof fisheries, wildlife and conservation biology who led the study withchemistry professor Thomas Hoye. "Also, lamprey are important to nativepeoples on the West Coast, who value it for food. This pheromone couldhelp restore lamprey runs by attracting lamprey to suitable spawningbeds."
When they stop feeding, lamprey seek out streams for spawning byfollowing the pheromone trails. After arriving at the spawning grounds,a sex pheromone -- which was identified by Weiming Li, an earlierdoctoral student of Sorensen -- attracts the females to males. Afterspawning, which takes a few weeks, the adults die.
It has taken Sorensen and his colleagues about 15 years to find,isolate and purify the pheromone so that Hoye and his colleagues couldidentify and synthesize it. The key component is a steroid with potencyso great that lampreys would smell a single gram dissolved in 10billion liters of water, enough to fill 5,000 Olympic-sized swimmingpools. This level of potency tops that of all other fish attractants,including those of salmon.
To find the pheromone, the researchers extracted 8,000 liters of waterfrom tanks holding 35,000 larvae. The yield was less than a milligram,or 35 millionths of an ounce. Much of the work in isolating andpurifying the pheromone was performed by Sorensen's graduate studentJared Fine, while Vadims Dvornikovs, Christopher Jeffrey and Feng Shaoin Hoye's lab were integral to synthesizing the key component, calledPADS. The chemical structure of PADS is very similar to that ofsqualamine, a compound made by the "dogfish" shark. Squalamine has beenreported to work against cancer by inhibiting the growth of bloodvessels that feed tumors but not other blood vessels. The other twocomponents of the pheromone are a second steroid and an already known,lamprey-specific bile acid derivative.
Until the pheromone can be synthesized in bulk, extracts of water fromlarval lamprey nurseries are being used to trap adults on anexperimental basis in Michigan streams.
"Using these extracts has been shown to work," said Sorensen. "Capturerates are up six-fold." Most lamprey traps have been simple, ratherineffective devices, but now the attractants have opened up many newpossibilities for attracting lampreys safely, easily and inexpensivelyinto streams, where they might be captured. In theory, the cue couldattract lampreys from many locations for miles around and could workfor as long as several months.
The work was supported by GLFC, the University of MinnesotaAgricultural Experiment Station and the National Institutes of Health.
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