Eels are snake-like fish that lack scales. There are around 800 species, ranging from some kinds just a few centimetres in length to the 3-metre (10-foot) giant moray. They have long, thin bodies with narrow dorsal fins that do not stick out from their bodies like those of other fish. Eels swim in a wave-like motion, called undulatory movement, that pulls their bodies into an S-shape (snakes move across land in a similar way). Eels live worldwide in oceans and rivers. Their young are called elvers.

Moray eel

Moray eels hide in holes between rocks or in coral crevices, waiting to shoot out and grab their prey—fish or octopus. The largest kinds of moray eel can grow up to 3 metres (10 feet) long. Morays have a second set of jaws in their throats. Called pharyngeal jaws, these are also lined with teeth. When feeding, morays launch these jaws into their mouth. These grab the prey and take it into the throat. Moray eels are the only animals that use pharyngeal jaws to capture prey.

European eels live in freshwater streams across Europe. An adult may grow up to 70 centimetres (more than 2 feet) long. When they are about six years old, they travel more than 6000 kilometres (3700 miles) out across the Atlantic Ocean to lay their eggs in the warm, still waters of the Sargasso Sea to the northeast of the Bahamas. Their young then drift back to Europe in the Gulf Stream, a journey that takes them about 10 months.

Gulper eel

The gulper eel is a two-metre-long eel with a gaping mouth and a light organ on its tail, used to attract prey. It can live at depths of up to 5400 metres (17,700 feet). It has huge jaws and a stretchy stomach that allows it to swallow animals that are larger than itself.