The snakelike fishes called eels live in fresh and salt water throughout much of the world. Hundreds of species of eel have been identified, and there is much variety among them. Adult eels range in length from just 4 inches (10 centimeters) to 11 ¹/₂ feet (3.5 meters). Deep-sea species tend to be gray or black, while tropical reef species can be colorful and patterned.

Where eels live

Eels can be divided into broad categories based on whether they live mostly in salt water or in freshwater. Most eel species are saltwater types that spend all of their lives in the sea. Two of the best-known types of saltwater eels are moray eels and conger eels. Morays live in tropical seas and are the most widespread of all the eels. Congers live mostly along the coasts of both tropical and temperate areas of the Atlantic Ocean. Freshwater eels can be found in the rivers, lakes, and ponds of almost every continent. They travel to salt water to reproduce.

Most eels like warm water. They seek out areas with many places to hide, such as muddy, rocky, or weedy spots. Many eels spend most of their time in cracks and crevices, using their flexible bodies to fit into small spaces.

Physical features

Eels have long bodies with a continuous fin that runs along the back and around the tip of the tail. Their heads are pointed, sometimes with a wide mouth and strong, sharp teeth. Most eel species have smooth bodies, but some have small, scattered scales deeply set in the skin. Eels change color throughout the different stages of their lives. As adults, common freshwater European eels are black on the back and silver on the sides and belly. Bright colors and patterns are typical of the morays.

Behavior

Adult eels are predators, meaning that they hunt other animals for food. Their prey includes shrimps, snails, fish, mussels, and worms. Most eels hide during the day and come out to hunt at night. Morays have been known to attack underwater divers, but they generally do this only when provoked.

Most eels swim slowly by wriggling from side to side. They generally live alone rather than in groups. Garden eels are unique in that they form vast colonies made up of hundreds of individuals. Each garden eel uses its tail to dig a tube down into the sandy ocean floor. It spends much of its life with the tail end of its body hidden in the tube and the head end waving above the ocean floor. A colony of these eels is said to look like a garden of swaying plants.

Freshwater eels have a special breathing technique that helps them during their migrations. They breathe through gills like other fish do, but they also can absorb oxygen through their skin. This ability allows them to move overland at night, gliding through damp grass for several hours at a time. In this way eels living in lakes and ponds can make their way to rivers that will take them out to sea.

Life cycle

Eels go through stages of development on their way to adulthood. Baby eels, known as leptocephalus larvae, hatch from eggs in the ocean. The larvae are typically broad, flat, and transparent, with sharp teeth. They are so different from adult eels that scientists once thought they were a separate species. The larvae drift with the ocean currents, growing larger while feeding on tiny life forms at the water's surface. After floating for as long as three years, the larvae end up very far from their birthplace.

As a larva nears land, it undergoes a series of rapid changes. It typically becomes round and loses much of its weight and its first teeth. These and other changes turn the larva into a young eel, or elver, which looks like a miniature adult eel. This process of change, called metamorphosis, prepares the eel for life in the environment in which it will mature. A freshwater eel and a deep-sea eel, for example, take on different traits needed for survival in the different habitats they will enter.

After a number of years the eels reach adulthood and are ready to mate. Adults of most species travel to a particular area to reproduce. The freshwater American and European eels swim to the Sargasso Sea, a part of the western Atlantic Ocean south of Bermuda. The journey is especially remarkable for European eels, which travel thousands of miles to reach the breeding ground. Similar central breeding places exist for other freshwater eels as well as some saltwater eels.

Relationship with humans

People in Asia and Europe eat eels, especially the freshwater varieties. In some countries eels are caught and then raised in captivity, where they mature faster than in the wild. Most eels caught in the United States are shipped abroad. Because many of the eels caught are babies, there has been some concern about the future of the American eel population. Closer regulation of the eel catch has been introduced to make sure enough young eels are left in the water to develop into adults capable of reproducing.