Eel, long slender fish of the order Anguilliformes, without pelvic fins and with dorsal and ventral fins joining the tail fin. The order includes the conger, moray, snake, snipe, and freshwater eel families. Some eels are covered in slime, and some have tiny scales on the skin. Moray eels live in warm water and are a danger to divers because of their bite. American and European freshwater eels spawn in the Sargasso Sea. The leaf-like larvae cross the ocean and enter rivers as young eels, or elvers. When adult, they swim back to the Sargasso Sea to spawn and die.