The European flounder, known scientifically as Platichthys flesus, is a marine flatfish inhabiting the coastal waters of Europe. This adaptable species distinguishes itself through its unusual anatomy and ability to thrive in diverse aquatic environments. Its presence spans a wide geographical range.
Distinctive Features and Where It Lives
The European flounder has a flattened, oval-shaped body, about half as wide as it is long, growing to around 30 centimeters, though some individuals can reach up to 60 centimeters in length and weigh up to 2.93 kilograms. Its most striking feature is its asymmetry; both eyes are located on one side of its head. The right side is more common (about 70% of individuals), but approximately 30% are “reversed,” with eyes on the left side.
The upper surface of the flounder is a dull brown or olive-green, often marked with reddish spots and brown blotches, allowing it to blend with its surroundings. This color-changing ability provides camouflage against predators and aids in ambushing prey. The underside remains a pearly-white, contributing to its common name, the “white fluke.” The lateral line features rows of small tubercles, as do the bases of its dorsal and anal fins, giving its skin a rough texture.
This adaptable flatfish is found in a wide array of aquatic environments, including freshwater, saltwater, and brackish waters. Its distribution extends along European coasts, from the White Sea in the north down to the Mediterranean and Black Sea in the south. European flounders are bottom-dwelling fish, preferring sandy and muddy seabeds in coastal waters, estuaries, and even venturing upstream into rivers and lakes. They reside at depths of up to 50 meters, moving into deeper, warmer waters during winter, sometimes up to 300 km offshore.
Life in the Water
The European flounder is a nocturnal creature, resting on the seafloor during the day, often semi-submerging itself in the substrate. Its diet consists of benthic invertebrates, such as bivalve mollusks, gastropod mollusks, crustaceans like shrimp, and polychaete worms. Adults also consume small fish, while juveniles less than a year old feed on plankton and insect larvae. They possess powerful teeth capable of crushing the shells of their prey.
The life cycle of the European flounder involves a transformation. Spawning occurs from March to June in the open sea, where females can release eggs ranging from 400,000 to 2 million. These eggs float to the surface and hatch within about a week. The larvae drift in open water, and during their development, one eye migrates across the head to the other side, transitioning the symmetrical larva into the asymmetrical, flat-bodied adult form. Growing larvae and early juveniles then migrate towards the coast, using selective tidal transport to move upstream in rivers.
Its Place in the Ecosystem and for Humans
Within its marine ecosystem, the European flounder plays a dual role as both a predator and a prey species. It contributes to the regulation of benthic invertebrate populations by preying on mollusks, crustaceans, and worms. In turn, it serves as a food source for larger predatory fish and marine mammals.
For humans, the European flounder holds significance in commercial fisheries, particularly in the Baltic Sea and the waters around the Netherlands and Denmark. In 2010, the total world catch was approximately 19,000 tonnes, primarily harvested through bottom trawling. The fish is marketed fresh and frozen, suitable for various culinary preparations. While not as highly esteemed as European plaice or common sole, it is still consumed.
The European flounder is also a popular target for recreational anglers. Despite its widespread distribution and abundance, the species is classified as “Least Concern” by the International Union for Conservation of Nature (IUCN), indicating no immediate threat to its populations. Ongoing monitoring of breeding habits and habitat preferences is important for its long-term sustainability.