The sea lamprey is an aquatic invader from the Atlantic Ocean that entered the Great Lakes through ship canals and locks built to bypass natural obstacles like Niagara Falls. An unintended consequence of these canals has been the introduction of invasive species like the lamprey eel. The sea lamprey was one of the first to invade the Great Lakes. It has been very damaging because part of its life cycle is spent feeding parasitically on the blood of host fish like the native lake trout. Sea lampreys are a very primitive, jawless fish. Although they are classified as a vertebrate, they lack bones and have only a cartilaginous rod or “notochord” for a spine. The paired fins found on most fish are also absent. The most remarkable feature of the sea lamprey is the toothstudded oral disk found at the anterior end. During the parasitic period of their life cycle, they use the oral disc like a suction cup to attach to the side of a host fish similar to the actions of a leech. The many teeth on the rim of the disc provide traction and make it very difficult for a fish to dislodge a sea lamprey. Once attached, they use the teeth on the tongue in the center of the disk to rasp through the skin. An anticoagulant in their saliva maintains blood flow as they feed. Often the host dies from the blood loss. Estimates of the number of pounds of fish killed by each sea lamprey vary from about 15 to 40 pounds.
Several characteristics of the sea lamprey made it an effective marine invader of the Great Lakes. First, the sea lamprey is an “anadromous” fish. This means that it spawns in fresh water streams, the juvenile phase is spent in salt water in the ocean (or one of the Great Lakes as a substitute), and the adult returns to freshwater streams to spawn. Special modifications of their kidneys allows these species to live in either fresh or salt water. Second, sea lampreys produce large numbers of eggs. Third, lampreys locate streams for spawning using a pheromone excreted by larvae. This pheromone identifies streams successfully producing young. Because the native lampreys also produced this pheromone, the larger, invading sea lampreys had an effective “road map” for expansion
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