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up to 60 centimeters


up to 2.5 kilograms


dark gray on the topside, white on the underside


up to 7 years


worms, crustaceans, shellfish




poeple, seals



  • Dut: Bot (Lovertje, Rivierschol, IJbot, But)
  • Lat: Platichthys flesus
  • Eng: Flounder
  • Ger: Flunder, Butt
  • Fren: Flet
  • Dan: Skrubbe (Flynder)
Flounder, Ecomare


Flounder is the only flatfish that migrates to freshwater without any problem. They have been found in the Rhine by Basel Switzerland. Their preference is to live in brackish waters. Should you find one flounder, you're bound to find more however they are so well camouflaged that they are difficult to discover. The eyes of this flatfish are usually on the right side but they are sometimes on the left.

  • Distribution
    Distribution of flounder, Ecomare

    Flounder spawn in salt water, but grow up in brackish water. They prefer brackish tidal waters and river mouths, but have no problem swimming upriver. In general, freshwater flounder migrate to sea to reproduce one year later than brackish water flounder.

  • Skin ulcers
    Skin ulcer in flounder, Ecomare

    Flounder often have ugly skin ulcers. They get these ulcers in various ways: from sudden transitions between fresh and salt water and poor water quality. In the 1980s, older flounder often had liver cancer. In 1985, as many as 30-40% suffered from this disease. The numbers dropped to 2% by 2004. According to scientists, this was due to a decline in toxic materials such as PAHs and PCBs. The quality of the seawater and the bottom along the North Sea coast has improved immensely since this decline.

  • Flounder fisheries

    Flounder used to be affluent in the brackish Zuiderzee, where there was a profitable fishery for this fish. However after the causeway was built in 1932, the fisheries crashed. Nowadays, there are still flounder in the IJsselmeer (the former Zuiderzee), but these are smaller than their cousins in brackish and salt water.
    Flounder are not fished very much in the Netherlands anymore because they have an earthy taste. No more than 2 thousand tons are landed yearly in Dutch harbors. However, it is still a commercially interesting species in the Baltic Sea.