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Fish

European Flounder

Platichthys flesus

European Flounder

Overview

The European flounder (*Platichthys flesus*) is an extremely adaptable flatfish (pleuronectiform), one of the few marine species that can tolerate very low salinity. It is renowned for its body asymmetry and remarkable camouflage ability. In the Black Sea basin, the flounder is a traditional fishery resource, valued for its white, delicate flesh.

Physical Characteristics

The body is strongly flattened laterally (disc-shaped), with both eyes usually on the right side of the head (the "coloured" side). The dorsal side is rough to touch due to small bony tubercles and has variable colouration, from brown to greenish, with orange spots. The ventral side (resting on the substrate) is white and smooth. It can rapidly change shade to blend perfectly with the seabed.

Habitat & Distribution

The flounder lives along European coasts, from the White Sea to the Mediterranean and Black Sea. It is a euryhaline species, allowing it to enter deep into river estuaries. In the Danube Delta, it is frequently found in the outlet zones of branches and in the Razim-Sinoe complex, preferring sandy or muddy substrates where it can bury itself partially.

Behavior & Feeding

It is a solitary, benthic fish. It feeds mainly at night, using smell to find invertebrates hidden in sediments: bivalve molluscs (which it crushes with pharyngeal teeth), polychaete worms, and small crustaceans. During the day it usually lies buried in sand, with only its eyes above the surface to watch its surroundings.

Life Cycle & Reproduction

Although it lives in coastal or brackish waters, the flounder migrates to the open sea to reproduce, as its eggs need a certain salinity to float. Newly hatched larvae are symmetrical, with eyes on both sides; as they grow, a spectacular metamorphosis occurs in which one eye migrates over the top of the head, and the fish begins to swim on one side.

Conservation Status

Classified as Least Concern (LC), the flounder remains a common species. However, the quality of its feeding habitats in estuarine zones is essential for maintaining populations. Sediment pollution and destruction of nursery areas are the main long-term risks.