American Eel (Anguilla rostrata)
Appearance The American eel is a long fish with tiny, almost unnoticeable scales. Its dorsal fin connects to the caudal (tail) fin and wraps around to the anal fin, giving the appearance of one long fin. Female eels often grow to 3 to 4 feet long; males rarely exceed half that length.
Habitat and habits American eels spend most of their lives in rivers, streams, and lakes. During daytime they seek out crevices in logjams, rip rap, or boulders. They will also burrow into sand and gravel, leaving only their heads exposed. At night they feed on frogs, fish, insects, and other aquatic animals. Other fish and birds such as bald eagles and cormorants eat them. Eels absorb oxygen through their skin, so they can survive for a time out of water. Sometimes they slither from one stream or lake to another. Native to the lower Mississippi, St. Croix, and Minnesota rivers, American eels are rare in Minnesota today. They also live in Lake Superior.
Ocean connection The American eel is catadromous, meaning that individuals of this species spend most of their lives in freshwater but travel to the ocean to spawn. This journey is one of the true wonders of the natural world. The origins and habits of American eels in Minnesota are not well known, but scientists think that our eels join other American—and even European—eels in the Sargasso Sea, a 2-million-square-mile floating mat of seaweed in the north Atlantic Ocean near Bermuda. To reach Minnesota waters, they must travel nearly 1,700 miles up the Mississippi, swimming through 18 locks and dams. They have even been known to crawl up the sides of dams.
Life cycle In the Atlantic, American eel eggs hatch into translucent larvae known as leptocephali. Leptocephali drift in the ocean for many months before metamorphosing into translucent, miniature versions of the adult called glass eels. Glass eels swim toward shore, gaining pigment upon entering freshwater rivers, such as the Mississippi. Most elvers, as the pigmented forms are known, migrate upstream, attracted by the odor of freshwater and decaying vegetation. As they grow, the elvers turn colors and earn a new name, yellow eel. After five to 20 years, yellow eels metamorphose into a form that is sexually mature and better adapted to ocean life. These eels, called bronze eels or silver eels, swim downstream and leave freshwater, presumably to return to the Sargasso Sea to spawn. Status The American eel is one of 292 species in greatest conservation need identified in the DNR conservation plan called Tomorrow's Habitat for the Wild and Rare. Most freshwater eels (Anguillidae) face serious threats, including overfishing, pollution, and habitat change.
Mary Hoff, freelance science writer