Some eels live in rivers, but most live in the sea, including moray eels and conger eels.
Moray eels are huge and live in tropical waters, where they hunt fish, squid and cuttlefish.
Gulper eels can live more than 7,500 m down in the Atlantic Ocean. Their mouths are huge to help them catch food in the dark, deep water — so big that they can swallow fish larger than themselves whole.
Every autumn, some European common eels migrate more than 7,000 km, from the Baltic Sea in Europe to the Sargasso Sea near the West Indies to lay their eggs.
Migrating eels are thought to find their way partly by detecting weak electric currents created by the movement of the water.
When European eels hatch in the Sargasso Sea they are carried northeast by the ocean current, developing as they go into tiny transparent eels known as glass eels.
The electric eels of South America can produce an electric shock of over 500 volts — enough to knock over an adult human.
Garden eels live in colonies on the seabed, poking out from holes in the sand to catch food drifting by. Their colonies look like gardens of weird plants.