European flounder

The European flounder (Platichthys flesus) is a flatfish that lives in European coastal waters. You can find it from the White Sea in the north all the way to the Mediterranean and the Black Sea in the south. Sometimes, it has been found in the United States and Canada because it was carried there accidentally in ships' water tanks.

This fish is usually oval-shaped and has its right eye on the top side. Most European flounders grow to about 30 cm long, but some can get as big as 60 cm. Their upper side is usually a dull brown or olive colour with reddish spots and brown marks, which helps them blend into the sand or mud on the ocean floor. The bottom side of the flounder is pearly-white, which is why it is also called the white fluke. The fish has special rows of tiny bumps along its body and near its fins, helping it sense its surroundings.

Description

The European flounder is a flatfish with an oval-shaped body. It can grow up to about 50 centimetres (20 inches) long. These fish are flat and usually rest and swim on one side. Most of the time, their eyes move to the right side, but in some fish, the eyes move to the left side instead.

The top of the flounder can be fawn, olive green, or pale brown with darker spots. The bottom side is pearly-white, which is why it is sometimes called a "white fluke". The fish has a small mouth and a rough skin with special features along its body.
lateral line
caudal peduncle

Distribution and habitat

The European flounder lives in the north eastern Atlantic Ocean and the Mediterranean Sea. It can be found from the Barents Sea, White Sea and Baltic Sea to Greece, Turkey, the Black Sea and the coast of North Africa. It has also been introduced to Iran and is now found along the eastern coast of Canada and the United States, likely arriving through ballast water. These fish live near the shore, usually in waters up to about 100 metres deep, on sandy or muddy bottoms where their coloring helps them hide.

European flounders can also live in estuaries, areas where rivers meet the sea, because they can tolerate less salty water. Unlike some other flatfish, they sometimes live in freshwater rivers. In the British Isles, they have been seen far inland in places like Montgomeryshire on the River Severn, Dinas Mawddwy on the River Dovey, and Garstang on the River Wyre. They eat food in the rivers and then swim back to the sea to lay their eggs.

Biology

The European flounder lives on the sea floor and in the water just above it. It mainly hunts for food at night and rests during the day, hiding partly under sand or mud. It eats small creatures like clams, shrimp, worms, snails, and tiny fish.

In the autumn, these fish leave freshwater areas and can be found in places where rivers meet the sea during cold weather. They then move to deeper water for the winter. In spring, they travel to special spots to lay eggs, moving about three to four miles each day without eating. The female releases about a million eggs that float, and the male releases sperm that also floats up. The eggs and sperm meet at the surface, where the eggs are fertilized and hatch in about six to eleven days, depending on the temperature. The baby fish drift toward the coast and into rivers and shallow waters. They grow quickly and become able to reproduce when they are still quite small.

Human interactions

The European flounder is eaten by people, but it is not as popular as the European plaice or the common sole (Solea solea). The most important places for catching these fish are in the Baltic Sea and near the Netherlands and Denmark. In 2010, people caught about nineteen thousand tonnes of European flounder, mainly using bottom trawling. These fish are sold fresh or frozen and can be cooked in many ways, like frying, boiling, steaming, baking, or microwaving.

Scientists have noticed that male European flounders living in polluted areas may show changes because of certain substances in the water. These substances were found in their blood at higher levels than in flounders from cleaner areas. However, the European flounder is not as affected by these substances as some other fish, like the freshwater rainbow trout.

Status

The European flounder is considered safe and not at risk by the IUCN in their Red List of Threatened Species. This is because there are many of these fish, and they live in a wide area. Though their numbers might be getting smaller, it’s not enough to worry too much. But in some parts of the Baltic Sea, changes have made it harder for them to have babies, and in places like the Gulf of Finland, they are almost gone, leaving another type of flounder called the Baltic flounder to be more common.