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Dieren en planten

Fish   Flatfish   Flounder   Fish biology   Reproduction of fish   Fish diseases   Marine fauna   Sea fish   Fauna in tidal areas   Fish   Freshwater fish   

Mens en Milieu

Pollution   North Sea   Wadden Sea   PCBs and BDEs   Pesticides   DDT   
Skin ulcer in flounder, Ecomare

Fish diseases

Fish have many more problems with diseases when the sea is polluted with toxic materials. For example, many fish swimming around with liver tumors is a sign that the water is polluted with PAHs. Flounder is a species of fish where extensive research has been performed in connection with liver tumors. Flemish marine biologists are also studying diseases in dab.

  • Flounder as the ideal patient

    Since 1983, fish species have been regularly studied at various locations along the coast for internal and external disorders. The benthic fish flounder in particular is being closely monitored. This fish species is a typical inhabitant of the coastal waters and river mouths, as well as several inland waters and the Wadden Sea. Adult flounder return every year to the same feeding grounds and remain for the entire summer. Flounder is exceptionally susceptible for specific diseases. Because contaminated materials move through the water close to the coast, this fish species is particularly suitable for studying these effects.

  • Wart disease

    The wart disease is a very commonly occurring virus infection. The virus incites connective tissue cells of the skin or fins to fester. Characteristic dirty white pearly lumps or warts form. It is not rare to find clusters of these lumps, resembling a tumor. The visible affliction can diminish or even disappear in time. However, the virus continues to slumber in the fish after healing and can be reactivated through natural causes or pollution. Studies on preventing this illness provide good opportunities for acquiring information on changes in the environment that affect the resistance in the fish.

  • Liver bumps and tumours

    Liver tumors and lumps are frequently found in flounder. There seems to be a link between the appearance of liver tumours in flatfish and the contamination from PAHs present in the sea bottom. This affliction is therefore used to study the effect of (carcinogenic) contamination in fish.

  • Open skin ulcers

    Flatfish can be seriously affected by open skin ulcers. This disease is often found in flounder in the direct vicinity of sluices in the Wadden Sea, the North Sea canal and the delta region.
    The abrupt transition from fresh and salt water makes the fish susceptible to such ulcers. If the sluices are managed in a different way so that the transition is more gradual then the flounder get fewer ulcers. Flounder can also get skin ulcers when caught and thrown back into the sea partially damaged. A link between environmental pollution and the occurrence of skin ulcers is not easy to demonstrate.

    Belgium biologists discovered a notable increase in diseased dab in the North Sea in the spring of 2011. Professional and sport fishermen both confirmed this observation. Many of the dab caught are infected with skin ulcers. The cause has not yet been determined.