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Lampreys have eel-shaped bodies, round, a sucking mouth lacking jaws, absence of paired fins, and seven external gill openings in a row on each side of the pharynx. About two dozen species occur in North America and Eurasia from the Arctic to subtropics and sub-Antarctic regions. Five kinds live in Great Lakes and tributary waters. All but the sea lamprey are strictly freshwater forms. Lampreys live in creeks, rivers and lakes. They ascend streams in the spring and usually nest on riffles, where they dig nests on which they spawn. The young hatch after several days and drift downstream until they become lodged in the bottom material. Lampreys spend several years as larvae, straining organic matter from the bottom. When they reach several inches in length they transform in late summer or autumn into adult-like lampreys with brownish, horny, teeth. The silver, chestnut, and sea lampreys are parasitic but the northern brook lamprey and American brook lamprey are non-parasitic. Parasitic lampreys attach themselves to fishes and suck nourishment from the host. Following one growing season as parasites they attain sexual maturity, spawn, and die. Brook lampreys do not feed, but live until the next spawning season, then reproduce and die. Sea Lampreys were first recorded in Lake Ontario in 1835, but the St Lawrence rapids were apparently too swift and Lake Ontario waters too cold for successful spawning. They became established in Lake Ontario as deforestation permitted warming, then spread from Lake Ontario through the Welland Canal in 1921 to Lake Erie and the upper lakes. In the 1940s populations became enormous, devastating lake trout in the Great Lakes. Control of the sea lamprey with larvicides has been only partly successful.
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