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Dieren en planten

Fish   Flatfish   Flounder   Fish biology   Fish communities   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

It has been shown that many poisonous materials weaken the antibody system in fish, whereby the fish become more suseptable to all kinds of diseases. Based upon historical data, there is strong evidence that around 1930, certain diseases such as liver tumours did not or hardly existed. Studies have shown that substances such as PAHs could evoke these tumours. The presence of fish with these liver tumours in the North Sea, even far from the coast, is therefore also cause for concern.

  • Studies of flounder

    Since 1983, fish species have been regularly studied at various locations along the coast for internal and external affections. The benthic fish flounder in particular is being closely observed. This fish species is a typical inhabitant of the coastal waters and river openings, as well as several inland waters and the Wadden Sea. Adult flounder return every year to the same feeding grounds and remain for the whole summer. Flounder has an exceptional susceptibility for certain affections. Because contaminated materials flow close to the coast, this fish species is particularly suitable for studying these effects.

  • Wart disease

    This is a very commonly occurring virus infection. The virus incites connective tissue to fester, particularly that of the skin. Characteristic dirty white pearly bumps or warts form on the skin and/or fins. It is not rare to find clusters of these bumps, which look like tumours. The noticeable 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 sickness provides good opportunities for acquiring information on these changes in the environment that affect the resistance in the fish.

  • Liver bumps and tumours

    Liver tumours and bumps 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

    Flounder can be seriously affected with open skin ulcers. The affliction is characterized by open wounds, which have a round form often with a white border of anaemic tissue. This disease is often found in the direct vicinity of sluices in the Wadden Sea, the North Sea Canal and the delta region.
    One suspects that a link exists between abrupt transitions from fresh and salt water, stress in flounder and susceptibility to skin ulcers. This suspicion grows stronger since improvements take place when the sluice management is change in such a way that the fresh-salt transition occurs more gradually.
    Other research shows that the susceptibility for skin ulcers can also be caused by the benthic fisheries, which often throw unwanted flounder overboard in a damaged state.
    A link between environmental pollution and the occurrence of skin ulcers is not easy to demonstrate.