May Control Parasite Fish
Sunday May 12, 2002 5:10 PM
CITY, Mich. (AP) - Disrupting the sea lamprey's mating
call may be the key to limiting its numbers in the Great
Lakes, where the eel-like parasite sucks the life out
of sport fish, scientists say.
secrete a smelly bile acid during spawning season that
draws ovulating females to nests, where they lay eggs
for males to fertilize, Michigan State University researchers
might lead to better trapping and sterilization programs
in the Great Lakes, where the lamprey is a pariah. But
it also could help produce more lampreys in places where
they are considered a delicacy - and it suggests that
sex lures might be used to raise or reduce other fish
research will help us produce new and more effective techniques
for sea lamprey control,'' said Chris Goddard, executive
secretary of the Great Lakes Fishery Commission, a U.S.-Canadian
agency that helped fund the study.
lamprey, native to the Atlantic Ocean, is believed to
have invaded the Great Lakes through shipping channels
in the early 20th century.
critter clamps its powerful disklike mouth onto the sides
of fish, digs in with sharp teeth and sucks their body
fluids. When satisfied, the lamprey releases its hapless
host, which usually dies from the wound or a later infection.
1950s, lampreys had decimated lake trout and wreaked havoc
with other popular species such as whitefish and sturgeon,
Goddard said. Control programs have cut their numbers
sharply in most of the Great Lakes, but they still do
published April 5 in the journal Science, labels the lamprey
invasion ``arguably the worst ecological disaster ever
to befall a large watershed.''
to five years in the larval stage, the lamprey spends
only a year to 18 months in its parasitic form before
moving into streams to spawn and die. But the typical
adult lives long enough to kill some 40 pounds of fish.
long suspected that males emitted a pheromone, or chemical
``message'' that guided females to nests, said fish physiologist
Weiming Li, who led the research team. The Michigan State
study confirmed the fact and helped explain how it happens.
captured sexually mature male lampreys and put them in
containers where they could secrete the chemical, manufactured
in their liver. Then, over two years, the scientists condensed
the water until they had a pure sample of the compound.
used behavioral tests, including placing females in a
maze, to show that the chemical is a sexual lure. They
found it is potent enough, and produced in sufficient
quantity, to attract females over long distances.
its molecular structure, the researchers learned how to
make synthetic versions of the chemical but still need
to find ways to do so less expensively, Li said.
presently control lamprey by sterilization, placing barriers
in streams to prevent spawning, and putting low concentrations
of a pesticide into streams to kill larvae.
discovered chemical could make it easier to capture lampreys
for sterilization, Li said. Also, spawning grounds could
be ``flooded'' with the chemical to confuse females, preventing
them from finding nests the males have built.
manipulate their movements into streams where you want
them and keep them out of streams where you don't want
them,'' said Dennis Lavis, supervisor of the U.S. Fish
and Wildlife Service biological station at Ludington,
which does lamprey control work.
pest control program needs a number of alternative methods,
and this research offers some very exciting possibilities,''
as promising for people who actually like lampreys. The
critter is a culinary delight in some countries, such
as Finland and France.
actually what got us started,'' Li said. ``French fishermen
used to bait traps with males to increase their catch.
We figured that perhaps this meant the males were releasing
Li is working
with a couple of American Indian tribes trying to restore
lampreys in the Columbia River and its tributaries. Once
scientists refine the use of the male bile acid, it might
improve the efficiency of hatcheries - or at least act
as a matchmaker for lampreys in the wild.
State report: http://ur.msu.edu/sealamprey