The female eel (up to 1.5 metres long and 4 kilograms in weight) is larger than the male (up to 1 metre long and weighing 1 kilogram). Adult eels have long and narrow bodies, with a continuous dorsal, anal and tail fin. The skin is slimy, the lower jaw is longer than the upper jaw, and the scales are tiny or absent. Adults can be brown, black or olive green, with yellowish bellies.
The common eel is found in rivers that empty into the North Atlantic, Baltic and Mediterranean Seas. It can also be found along European coasts from the Black Sea to the White Sea in Russia.
The common eel is a rare example of a “catadromous” species – that is, one that breeds in the sea and then migrates to fresh water to grow before returning once again to the ocean. It is thought that all European eels spawn in the Sargasso Sea in the Western Atlantic. The larvae drift among plankton for up to three years and are carried by the Gulf Stream towards the coasts of Europe. They then metamorphose into “glass eels”, so called because of their transparency. They then become darker in colour and begin to migrate up freshwater streams in large numbers. The eels grow there, with males and females spending six to 12 years and nine to 20 years respectively in fresh water. They then migrate back towards the sea and are known during this phase as “silver eels”. They can survive out of water for several hours on damp nights, and sometimes travel overland on dark, rainy nights. This species has a maximum lifespan of 85 years. They feed on insect larvae, small fish, frogs, crustaceans and molluscs.