Pheromones may be used to herd alien fish

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A primitive aquatic beast that has decimated fish stocks in the North American Great Lakes could soon be lured into traps using a migratory pheromone.

“This is the first time that a vertebrate pheromone has ever been applied for control,” says biologist Peter Sorensen at the University of Minnesota in St Paul, US.

Cylindrical, boneless sea lamprey (Petromyzon marinus), which evolved before the dinosaurs, can have a catastrophic effect on fish populations. Half-parasite and half-predator, their teeth sprout from their tongues and line the edge of their mouths. They sink them into the sides of almost any other fish and suck out their bodily juices until they die. “It’s pretty horrific,” says Sorensen.

Sorensen’s team has worked out exactly which three compounds make up a pheromone released by lamprey larvae that attracts adult lamprey in the wild. One of the three - petromyzonol sulphate - was known to be part of the pheromone, but petromyzonamine disulphate or “PADS” and petromyzosteral are totally new.

Aquatic maze

The team has also synthesised PADS, the most potent of the three compounds, and used it to herd the prehistoric fish down one side of a two-channel, 10-metre-long aquatic maze in the laboratory. Lamprey have evolved to follow the pheromone at a particular point in their lifecycle because it guides them to suitable spawning streams.

“There is a whole suite of possible applications,” says Michael Twohey of the US Fish and Wildlife Service in Marquette, Michigan. “The migratory pheromone has the opportunity to reach out into a portion of the Great Lakes and attract them into one stream at the expense of another. You could protect a particular river from a migration.”

The Great Lake Fisheries Commission, based in Ann Arbor, Michigan, US, is desperately seeking new methods to control lamprey populations. The fish destroyed the Great Lakes’ fishing industry in the 1930s after they were brought there on the hulls of ships that travelled along new canals linking the Atlantic Ocean - their natural home - to the lakes.

Toxic threat

Lamprey control is currently based on a toxic, larvae-killing compound known as TFN. This is dumped into the freshwater streams where lamprey spawn. Discovered in the late-1950s, this has at least brought recreational fishing back to the lakes, although many species are still extinct there, says co-author and chemist Thomas Hoye.

But the compound is toxic and could be banned if environmental groups sue. “People get upset, they don’t want poisons in drinking water,” says Sorensen. Another possibility is that the fish could develop resistance to it.

The commission has set a goal to reduce the reliance on TFN. It has experimented with several alternatives, including erecting cement barriers to cut lamprey off from spawning grounds and sterilising males.

Pheromones are an attractive alternative because they are not toxic and likely to be cheap, because extremely little is required. Sorensen reports that a PADS concentration of just one part per 10 trillion is needed to herd the fish.

Sex pheromone

Twohey says a sex pheromone released by male lamprey to attract females could also be used to herd the prehistoric creatures. But the two would work at different stages of the fish’s life cycle.

Ironically, pheromones could also be used to replenish lamprey populations in the Atlantic ocean off the coast of Europe, where it is prized as a delicacy but has been fished close to extinction. Hoye also suggests that herded and trapped great lake lamprey could be sold for food to Portugal and Finland.

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I hope this works... nasty little buggers. I saw my first one in 8th grade that was caught out of the river near by. Kept me out of the water for a long time after that.