European flounder

The European flounder (Platichthys flesus) is a flatfish of European coastal waters from the White Sea in the north to the Mediterranean and the Black Sea in the south. It has been introduced into the United States and Canada accidentally through transport in ballast water. It is caught and used for human consumption.

The European flounder is oval in shape and is usually right-eyed. It normally grows about 30 cm in length, although lengths of up to 60 cm have been recorded. The upper surface is usually dull brown or olive in colour with reddish spots and brown blotches and this fish can change colour to suit its background, providing an effective camouflage. The underside is pearly-white, giving the fish one of its common names, the white fluke. The lateral line features rows of small tubercles, as do the bases of the dorsal and anal fins.

Distribution

The European flounder is native to the north eastern Atlantic Ocean and the Mediterranean Sea. The range extends from the Barents Sea, White Sea and Baltic Sea to Greece, Turkey, the Black Sea and the North African coast. 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.

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 British Isles, it has been found as far inland as Montgomeryshire on the River Severn, Dinas Mawddwy on the River Dovey and Garstang on the River Wyre. Unlike the Atlantic salmon, it feeds in the rivers and makes its way out to sea again before spawning.