American Eel

American eels can grow to 1.22 m (4.0 ft) in length and to 7.5 kg (17 lb) in weight. Females are generally larger than males, lighter in color, with smaller eyes and higher fins. The body is elongate and snake-like. Its dorsal and anal fins are confluent with the rudimentary caudal fin. It lacks ventral fins but pectoral fins are present. The lateral line is well-developed and complete. The head is long and conical, with rather small, well-developed eyes. The mouth is terminal with jaws that are not particularly elongated. The teeth are small, pectinate or setiform in several series on the jaws and the vomer. Minute teeth also present on the pharyngeal bones, forming a patch on the upper pharyngeals. Tongue present with thick lips that are attached by a frenum in front. Nostrils are superior and well separated. Gill openings are partly below pectoral fins, relatively well-developed and well separated from one another. Inner gill slits are wide. The scales are small, rudimentary, cycloid, relatively well embedded below the epidermis and therefore often difficult to see without magnification. The scales are not arranged in overlapping rows as they often are in other fish species but are rather irregular, in some places distributed like "parquet flooring". …

The distribution of the American eel encompasses all accessible freshwater (streams and lakes), estuaries and coastal marine waters across a latitudinal range of 5 to 62 N. Their natural range includes the western North Atlantic Ocean coastline from Venezuela to Greenland and including Iceland. Inland, this species extends into the Great Lakes and the Mississippi River and its tributaries as far upstream as Minnesota and Wisconsin. Nonindigenous occurrences of this species in the United States were recorded from Lake Mead on the Colorado River and on the Arizona border. It was stocked on a few occasions in Sacramento and San Francisco Bay, California, in the late 1800s. No apparent evidence of survival on these occasions was noted. It was also stocked and unintentionally introduced in various states, including Illinois, Indiana, Nebraska, Nevada, North Carolina, Ohio and Pennsylvania. Stockings of this species also occurred in Utah in the late 1800s, but soon disappeared.

The American eel's life cycle begins far offshore in the Sargasso Sea in a semelparous and panmictic reproduction. In 1926 Marie Poland Fish described the collection of eggs that she observed hatch into eels, which she expanded in her taxonomic description of the larval egg development. From there, young eels drift with ocean currents and then migrate inland into streams, rivers and lakes. This journey may take many years to complete with some eels traveling as far as 6,000 kilometers. After reaching these freshwater bodies, they feed and mature for approximately 10 to 25 years before migrating back to the Sargasso Sea in order to complete their life cycle.The eggs hatch within a week of deposition in the Sargasso Sea. Fecundity for many eels is between about 0.5 to 4.0 million eggs, with larger individuals releasing as many as 8.5 million eggs. The leptocephalus is the larval form of the eel. Leptocephali are transparent with a small, pointed head and large teeth. The laterally compressed larvae are passively transported west and north to the coastal waters on the eastern coast of North America, by the surface currents of the Gulf Stream system, a journey that will last between 7 and 12 months. As they enter the continental shelf, leptocephali metamorphose into glass eels (juveniles), which are transparent and possess the typical elongate and serpentine eel shape. …