Scientists discover new way to control
parasitic fish in Great Lakes
By Susanna Quick
Milwaukee Journal Sentinel
Posted on Kansascity.com on October 3, 2005
MILWAUKEE - (KRT) - First they tried to block them out,
erecting walls and barriers to prevent the slippery, eel-like
bloodsuckers from migrating up rivers to spawn. But that
Then wildlife officials tried to poison the exotic sea
lampreys, dousing them with a toxic shower of chemicals
as the toothy fish wriggled over their riparian spawning
beds. But that practice provoked opposition and sometimes
proved deadly for invertebrates and cartilaginous fish
caught in the chemical cloud.
Now researchers believe they may have found a new tool
to help control and reduce the population of Great Lakes
Scientists at the University of Minnesota have identified
and synthesized a powerful pheromone that may be used
to lure large numbers of adult lampreys to their deaths.
The research was reported in Sunday's online version of
Nature Chemical Biology.
"I'd say this is pretty important stuff," said
Henry Quinlan, a fisheries biologist at the Ashland fishery
resources office of the U.S. Fish and Wildlife Service.
"It's another potential tool for sea lamprey control.
It's certainly exciting."
The Atlantic sea lamprey is a non-bony, parasitic fish
that was first noticed lurking in Lake Erie in 1921. Now
in each of the Great Lakes, the foreign pest has sucked
fluids from fish such as lake trout, whitefish and herring,
decimating and in some cases destroying these ecologically
and commercially important fisheries.
For more than 50 years, wildlife officials have tried
to control the situation. And while they believe they
finally have a handle on the problem - with the use of
the chemical TFM, a lampricide that selectively kills
the creatures in the larval stage when applied to tributary
streams - they'd like to do more.
This is where the new research comes into play.
Trained in the biology and physiology of fish-smelling,
Peter Sorensen, a professor of fish biology at the University
of Minnesota, started in 1990 to look at the lamprey's
chemical and olfactory repertoire.
Nearly 400 million years old, lampreys, like many other
ancient sea creatures, tend to rely heavily on chemical
cues for communication. Indeed, the lamprey's "nose,"
or its sensory epithelium, exceeds the size of its brain.
Sorensen figured if he could identify the chemicals that
the lampreys were using to call one another, he might
be able use their own bodily secretions against them.
Sea lampreys reproduce in freshwater streams, where their
larvae spend three to 20 years. Toothless and blind, the
larval lampreys burrow into the river bottom, stretching
their heads up into the current where they open their
fleshy, hooded mouths wide to feed on the detritus that
At some point, they disengage themselves from their muddy
holes and transform into free-swimming juveniles. During
this metamorphosis, they lose their hood, grow eyes and
develop a set of teeth on their tongue and "sucking
disk" - a flat, disk-shaped area that surrounds their
Now called transformers, the silvery, pencil-length juveniles
catch the current downstream to the lake, where they start
sucking juice and blood from fish.
The average sea lamprey may kill as many as a dozen lake
trout - totaling 40 pounds - during its one- or two-year
stay in open water. The duration of attachment on a fish
varies, but the site of attack, time of year and size
of lamprey all help determine whether the assault will
When the lamprey matures, it starts to seek out suitable
rivers for spawning. Unlike salmon, which return to their
streams of birth, lampreys look for streams that have
This is where Sorensen's work comes in. It appears that
the odor of healthy larvae attracts adults to specific
The odor is so powerful, said Sorensen, that one of his
graduate students discovered that a single larva could
activate hundreds of gallons of water.
That fact alone indicated to Sorensen that this odor
might be potent enough to attract adults in the massively
diluted environment of one of the Great Lakes. The next
step was to find out what the pheromone was.
He and students in his lab took larval-tainted water
samples and removed chemical compounds within it. Sifting
through these compounds, they isolated three they believed
to be involved in the pheromone.
They were able to identify one of the compounds, but
the other two were a mystery. So they contacted Thomas
Hoye, a chemist at the university.
Hoye told Jared Fine, one of Sorensen's graduate students,
that he'd need an ample amount of the pheromone to identify
"So, Jared rolled up his sleeves, and dug into 8,000
liters of water - that's 2,000 gallons - that had held
35,000 larvae. He came to me with a couple of samples,
which weighed less than a milligram. That's the equivalent
of 10 grains of salt," Hoye said. But it was enough.
They identified the compounds, and then needed to synthesize
They did that, but to make the chemical a useful management
tool, they'll need to figure out a way to synthesize it
more efficiently, Hoye said.
"Think of Lewis and Clark," he said. "They
set out to find a way to get to the Pacific. They went
down dead-end rivers and had to come back. But they got
there, even if it wasn't the most efficient way. Somebody
else had to come along and find a more effective way to
get through to the Pacific_to get their carriages through
the mountain range more easily."
That's the next step for Hoye and Sorensen - to figure
out how to make large quantities of this chemical easily.
Sorensen said field work has already begun using the
pheromone. Trials conducted by the Great Lakes Fishery
Commission in Ann Arbor, Mich., started this summer. Fish
managers discovered that the pheromone worked well.
Splitting a stream in two - one run laced with pheromone,
the other without - they found that the treated side brought
in as many as seven times the number of adults as the
untreated run, Sorensen said. That research is not yet
It is believed the pheromone will be used to attract
lampreys to specific streams and traps where they can
be removed or poisoned. It may also become a useful conservation
tool in areas of the Atlantic and North Pacific where
the sea lamprey is endangered.
If the pheromone could be synthesized at reasonable cost,
it might allow fisheries workers to virtually eliminate
sea lampreys from the Great Lakes through intensive trapping,
said Bill Horns, Great Lakes fish biologist for the Wisconsin
Department of Natural Resources. Because the U.S. and
Canadian governments spend more than $10 million a year
to control lampreys by other means, and lampreys still
damage fisheries, "that would be a major development,"
Hoye suggested that the trapped lampreys could be shipped
to Finland and Portugal, where they are considered delicacies.