True Eels

The freshwater eels, comprising about 16 species, are the most familiar family of eels to most people. These fish have an unusual characteristic in their life history, known as catadromy, in which the fish spend most of their lives in fresh waters, but run to the ocean to spawn.

The common freshwater eel of North America is the American eel (Anguilla rostrata). The European eel (A. anguilla) of western Europe and the Japanese eel (Anguilla japonica) of the north Pacific coast are closely related to the American eel. Relatively large numbers of eel species, about 12, occur in the Indo-Pacific region.

A green moray eel (Gymnothorax funebris). The eel has blue skin covered with a yellow mucus that renders its apparent color green. It can reach a maximum length of 6 ft (1.8 m). Photograph by J.W. Mowbray. The National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission.

The American eel can reach a length of about 4 ft (1.2 m). This species is abundant in freshwaters that link directly to the ocean. This range includes coastal rivers, and the larger drainage of the Saint Lawrence River, extending inland to Lake Ontario and to a lesser degree, the upper Great Lakes. There are no freshwater eels on the west coast of the America, or on the east coast of South America.

American eels spends almost all of their life in fresh waters. However, to breed, this species of eel runs to the sea and migrates to a warm-water region between the West Indies and Bermuda that is known as the Sargasso Sea. European eels also commonly spawn in the Sargasso Sea, following a migration of 4,000 or more miles (6,440 km). After spawning, the adult eels die. The baby eels, or elvers, are leaf-shaped and transparent, and migrate to fresh waters, where they transform into miniature but transparent replicas of the adult body form, sometimes known as "glass eels." These small fish then run up rivers, and take up residence in still waters of large rivers and lakes, where they live as adults for as long as 15 years.

This unusual breeding strategy was discovered only relatively recently. For many centuries, naturalists pondered the fact that they could never find spawning or larval eels, and the breeding habits of these fish were a mystery. It was not until 1922 that newly hatched eel larvae were observed, in the Sargasso Sea.

Freshwater eels are an economically important species of fish, and are particularly appreciated as a food in France, Belgium, The Netherlands, and Great Britain.