They kill other fish by attaching onto them with their circular mouths and sucking out the fluids. Sea lamprey have wreaked havoc on fish in the Great Lakes since the early 1900s, when the species first found a route around Niagara Falls. During the 1940s it killed nearly all the other fish species in the Great Lakes. Currently the Great Lakes Fishery Commission, a combined effort of the Canadian Parliament and United States Congress, is responsible for re-stocking the lakes with fish and administering pesticide to lamprey spawning areas. But some University researchers think they may have a way to control the sea lamprey without the large amount of pesticides currently used.
Pheromones are bile compounds found in the gall bladders of lamprey larvae.
Sorensen said it's possible that odors released by the lamprey larvae may attract adults to particular streams. Sea lamprey pick fewer than 100 streams off the Great Lakes in which to spawn. In theory, specific pheromones could be used to lure lamprey to streams where they couldn't mate, or to places where male lamprey could be sterilized or where lamprey could be killed. He said it's logical for sea lamprey to rely on smell because they have no sense of taste and develop cataracts in their eyes as they get older. But, like many other kinds of fish, they have a sense of smell.