Geographic variations in tumor prevalence among marine fish populations.

A global epidemiological study on the frequency of skin papillomas among various flatfish species (Pleuronectids), papillomas of eels and the virus induced lymphocystis disease has revealed particular distribution patterns. Skin papillomas are prevalent among at least 20 flatfish species of the northern Pacific Ocean, Bering Sea, Sea of Okhotsk, and Japan Sea but appear to be absent from the Atlantic, North Sea, and the Caribbean Sea. The opposite is found for lymphocystis, which is common among flatfish species of the Atlantic shores of Europe and North America. Similarly the skin papillomas of eels are restricted to relatively small region along the European coast extending from the Baltic countries to Denmark, Germany and Holland. Superimposed on this global distribution pattern are local variations in tumor prevalences which can vary from about 58% to 0.01%. The geographic distribution pattern points to the existence of areas around the globe in which flatfish or eels are able to develop skin papillomas. Outside these areas of "potential skin papilloma risk," flatfish and eel populations are not afflicted with papillomas even if they inhabit estuaries or rivers with a high man-made or naturally-occurring pollution.