January 20, 2009

Pheromones Used To Control Vampire Fish Colonization

Scientists say a synthetic chemical sex smell could help rid North America's Great Lakes of a devastating pest known as the "vampire fish."

A laboratory version of a male sea lamprey pheromone was deployed to trick ovulating females into swimming upstream into traps, US researchers said.

The vampire fish, known formally as the sea lamprey, has become a harmful parasite to native species of the Great Lakes since its accidental introduction in the 1800s.

Recreational fishing of the Great Lakes on the US-Canada border brings in billions of dollars a year. A lamprey control program costing about $20 million annually has been enacted to keep the parasites from damaging fish populations.

This marks the first time researchers have used pheromones as the basis of a possible way of controlling animal pests other than insects.

Lead researcher Weiming Li from Michigan State University in East Lansing, said there's been extensive study of pheromones in animals and even in humans.

Li told BBC news that most researchers have presumed that as animals get more complex their behavior is regulated in a more complex way, not by just one pheromone.

The research team released the synthetic version of a lamprey hormone from a trap placed in a stream where lampreys come to breed. Once the females picked up the scent, they would swim vigorously upstream until they found the source, becoming trapped in the process.

The vampire fish's natural life cycle takes it from birth in a stream to adulthood in the ocean.

The creatures possess circular jaws that can lock on to larger fish, where they then use their sharp tongue to carve through the fish's scales. The lamprey feeds on the blood and body fluids of its temporary host, often killing it in the process.

Eventually, both adult male and female lampreys swim back up stream to breed and die.

Contrary to salmon life cycles, which seek out the stream they were born in, lampreys appear willing to take any stream indicating a suitable breeding place. Scientists believe pheromones may play a role in identifying streams worth selecting.

The lamprey's numbers are controlled by predation in their native Atlantic Ocean, but they have no predators in the Great Lakes.

The so-called vampire fish first appeared in the 1800s after completion of the Erie Canal linking the lakes to New York.

They officially colonized the areas a century later when other canals provided unfettered access to the upper lakes, decimating native fish populations.

Marc Gaden from the Great Lakes Fishery Commission (GLFC), the body responsible for controlling the lamprey problem, called the pest's arrival one of the worst things to hit the Great Lakes in the history of European settlement.

"Before it, we had a thriving fishery largely dependent on native fish such as the lake trout... but by 1940 they had colonized thousands of streams and fishermen were beginning to see the devastation."

Unlike salmon, which have a set migration between fresh water and salt water, the lamprey appears to have thrived on its move from the saline Atlantic to the fresh environs of the five lakes.

An individual vampire fish can devour up to 45 pounds of trout or other host fish throughout the span of its lifetime.

A complex set of control measures have been established to control populations, including dusting the streams with pesticides specific to the lamprey, building barriers to block their upstream migration, and releasing sterile males to reduce breeding, the GLFC said.

Gaden said his team views the pheromone work as another tool in the arsenal.

"We see it as away of tricking these spawning lampreys, and then you can do things to manipulate their behavior in ways that would work against them - for example you could lure them into streams without suitable spawning habitat, or just into traps."

A larger experiment is still in the planning stages for Li's team.

They're currently undertaking a 3-year plan to use the pheromone to trap female lampreys in 20 streams feeding into the lakes.


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