The lateral line features rows of small tubercles, as do the bases of the dorsal and anal fins.

The lateral line is nearly straight and runs along the middle of the upper surface, curving round the short pectoral fins.

The skin is rough, with prickly tubercles at the base of the dorsal and anal fins, and there are large scales beside the lateral line.

[3][4] The European flounder is native to the north eastern Atlantic Ocean and the Mediterranean Sea.

It has been introduced into Iran and has become established off the eastern coast of Canada and the United States, possibly getting there by way of ballast water.

It is normally found from the low shore down to depths of about 100 metres (330 ft) on sandy, shingle or muddy bottoms where its dappled colouring camouflage it and make it difficult to detect.

[1] The European flounder can also be found in estuaries where it is tolerant of low salinity levels and, unlike other species of Pleuronectidae, it often spends part of its life cycle in freshwater and regularly makes its way into rivers.

In the spring it migrates to the spawning grounds, travelling at three to four miles (five to seven kilometres) per day and not eating en route.

The developing larvae are planktonic and drift towards the coast and use selective tidal stream transport to migrate into estuaries and rivers.

[6][7] Juvenile flounders live in shallow waters, estuaries and rivers commonly at low salinity conditions.

[8] It has been found that male European flounders living in polluted estuaries may show signs of excess exposure to oestrogens.