Sea lamprey 'love signal' may tame species

Sea lampreys feed by attaching on other fish with their suction-like mouths and extracting body fluids.

EAST LANSING, Michigan (CNN) -- Male sea lampreys -- eel-shaped fish that use their suction-cup mouths to extract body juices from other fish -- excrete a chemical during spawning that acts as a powerful sexual come-on, scientists at Michigan State University say in the journal Science this week

The discovery of the bile acid excretion could lead to new ways of manipulating sea lamprey populations, said Weiming Li and his research team. The chemical is detectable some 200 feet downstream, he said.

"The pheromone was suspected for quite sometime, but we were never sure of the structure and function, or which fish was releasing it," said Li, an assistant professor in the Fisheries and Wildlife department at Michigan State. "This discovery will have an impact on the basic understanding of chemical communication in aquatic animals, and will be useful in methods of population control or restoration."

Sea lampreys are native to the Atlantic Ocean. The parasitic species invaded the Great Lakes after the construction of the Welland Canal in 1829. Shipping channels became viable waterways for lampreys, and by the 1940s Lake Michigan's trout population was dwindling because of the invasion.

CNN NewsPass VIDEO Watch a video of spawning sea lampreys and the building of the nest in a spring over a stony bottom (April 4) Play video

The Great Lakes Fishery Commission, a joint U.S.-Canada venture established in 1955, has been fighting the problem. The commission funded Li's research.

"The sea lamprey is the poster child when it comes to aquatic nuisance species," said Li. "Each one will damage 40 to 50 pounds of high quality fish like salmon or trout in its lifetime. They are very destructive."

Sea lampreys use suction disk mouths to latch on to other fish. They then cut open the host fish with sharp teeth and suck on its bodily fluids. The host fish is often scarred or killed as a result. After the parasitic stage of its life, sea lampreys return to streams to spawn.

Unlike creatures that spermeate -- produce sperm -- most of their lives, sea lampreys, which live anywhere from five to 20 years, can only spermeate during the last two weeks of their lives. They spawn in streams in springtime, and the males arrive much earlier than females. The males build horseshoe-shaped nests, and then release pheromones to lure the females. The chemical come-on is produced in the male's liver.

A delicacy in Europe

In Europe the female sea lamprey is considered a delicacy. There, the discovery of this lamprey love potion may lead to ways of restoring the population in areas where the sea lamprey has become scarce. According to Li, French culinary taste for sea lamprey was integral in his research.

"In the 1930s, there were reports that French fisherman would use males to bait their traps to catch females," Li said. "It was suspected that some kind of pheromone was at work."

Michigan State University researchers' discovery of a chemical that acts as a sexual come-on by lampreys may lead to new efforts in controlling the eel-shaped fish population.

John Teeter of the Monell Chemical Senses Center in Philadelphia built on the premise in the 1980s. Teeter's work showed that sea lampreys were indeed attracting each other through chemicals or pheromones. Li studied under Teeter, then started his own lab at Michigan State in 1998, building on Teeter's work.

"If you look at these animals, they are really slimy and ugly, but they have quite a romantic language," Li said. "We spent 4 years trying to decode this language."

Li and his researchers spent the entire first year of the project trying to pinpoint in which fish and at what maturation state the chemical is released. The team found that only spermeating males produce the bile acid compound.

"If only the animals that spermeated produced this compound, then the compound that is unique to the spermeating male is most likely the pheromone, " Li said. "By that reasoning, we quickly identified the compound."

Once the compound was identified, Li began concentrating it. The process took over two years, as Li's team condensed water from tanks holding spermeating males. From more than a ton of water, they were able to collect approximately 30 milligrams of purified compound -- or about 1 drop. The purified compound was analyzed to identify the chemical structure. Li then worked with chemists to create a synthetic compound in the lab. Li said it is an exact match.

"It is so potent that we believe this synthetic compound can be applied in the control of sea lamprey population," Li said.

Field testing of the compound has not yet been scheduled.