The European conger is the heaviest of all eels. Eels are elongated fish, ranging in length from 5 cm ( in) in the one-jawed eel (Monognathus ahlstromi) to 4 m (13 ft) in the slender giant moray. Adults range in weight from 30 g ( oz) to well over 25 kg (55 lb). They possess no pelvic fins, and many species also lack pectoral fins. The eel is a long, thin bony fish of the order Anguilliformes. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was a mystery for a very long period of scientific history. Although more than publications mention eels, much of their life history remains an enigma.
Eels have a remarkable life cycle. Broadly, it consists of development and early growth in the open ocean: the planktonic (free-floating) dispersal of eggs and larvae, metamorphosis, juvenile and adult growth, and the migration of maturing adults to an oceanic spawning area. "Eel larvae have been observed in the Sargasso Sea since , suggesting that the species reproduced in this area, but no adult eels had ever been observed in this part of the Atlantic Ocean.
American eels are the only species of freshwater eel found in North America. They live along the Atlantic coastline from Venezuela to Greenland and Iceland. Eels can also be found in the Great Lakes and Mississippi River (Figure 1). Eels have a complex lifecycle that begins far offshore in the Sargasso Sea where adults spawn.