Eels are snakelike fish with elongated bodies and shallow fins. They can be found in both fresh and saltwater, depending upon the species, although all breed in salt water. Many species of freshwater eel are consumed by humans, and the fish is popular in European and Asian cuisines. Some species harvested by humans are under threat, and several nations have undertaken measures to ensure the health of their stocks.
The eel is a very peculiar fish, with an imperfectly understood life cycle. All spawn at sea, many of them in the Sargasso Sea. The larva drift with the currents as they mature into young, called glass eels, a totally transparent form. Glass eels are often found coastal areas and, in the autumn, they move into estuaries, where they turn into pigmented young known as elvers. Elvers migrate upriver, often over very long distances, and many species spend their entire lives in fresh water. In this stage, the fish are known as yellow eels and will reach a mature length which can range between 2 and 5 feet (0.5 and 1.5 meters) in length, depending upon the species.
When the fish reach sexual maturity, they undergo additional physical changes, turning gray with a pale belly. The pectoral fins and eyes of the eel enlarge, presumably to assist the fish in its migration back to the spawning area at sea, where it will die after mating. Since scientists have not actually witnessed the spawning process, biological information about the early life of eels is primarily conjecture.
Some eels, such as the moray, spend their entire lives at sea, lurking in crevasses and deeper ocean water. The moray is a well known family, because members tend to be vicious and are equipped with extremely sharp teeth that have been known to chip bone. Swimmers are encouraged to avoid morays, although they can be perfectly harmless and even friendly if they do not feel threatened. Many fish have the common name of eel, such as electric eels, although they are not in fact part of the Anguilliformes order.
Freshwater eels are commercially fished by several nations, and the global stocks of the fish are in decline. This may partially be due to the fact that the fish can take up to 20 years to mature, and some countries may have fished out their stocks of potentially viable mature eels. Because the life of the eel is not fully understood, the damage caused by commercial fishing may be more severe than was originally thought. Several nations are working together to conserve and rebuild their stocks, since the eel provides vital economic and cultural benefits to many countries.