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What disease is this?"The bass look as thought they may have lymphocystis. The walleye looks more like a dermal sarcoma or a bacterial lesion". Joe Marcino DNR Pathologist Two highly visible skin diseases which often cause concern among anglers. These diseases, known as lymphocystis and dermal sarcoma, are both caused by viruses but neither pose a health threat to people. April and May are the peak months for the appearance of lymphocystis. This disease is frequently seen by boat anglers in May and June. Lymphocystis usually appears as a cluster of white or cream-colored warts or fleshy growths erupting from the skin or fins of a walleye. A pinkish or red color may be present due to abrasion or hemorrhage. The disease has also been found to infect internal organs although this is quite rare. Lymphocystis is caused by a virus which is released into the water when growths on an infected fish rupture. The virus can infect healthy walleye by entering skin abrasions or cuts and then attacking cells in the connective tissue. These cells grow to a millimeter or more in diameter, gigantic as far as cells go;causing lumps on the skin which feel somewhat like a raspberry. Eventually these growths will rupture, releasing more virus particles into the water, and the lesions will become scarred over. Various authors differ on the incubation period of lymphocystis. Some report that a fish infected in the spring will develop growths the following spring. Others indicate that incubation may take only a few weeks. Temperature may be an important factor in determining this period. Dermal sarcoma may be less seasonal than lymphocystis but since the two diseases are often confused its frequency of occurrence is not yet known. A 1976 Canadian study examined 50 tumors which were thought to be lymphocystis and found twice as many dermal sarcomas as lymphocystis tumors. Examination with a magnifying glass will usually separate the two diseases. Lymphocystis tumors are composed of a few grossly enlarged cells. Dermal sarcomas consist of irregularly shaped but normal-sized cells. Both diseases can infect the same fish concurrently and, in some cases, both diseases have been seen in the same tumor. Yet they are caused by distinctively different viruses; two viruses which have not been found to exist together in the same cell. At least 65 species of freshwater and saltwater fish are known to contract lymphocystis. Lymphocystis and dermal sarcomas are not generally fatal to the infected fish. Practically all will recover from their infections. Anglers need not worry if these growths are seen on their walleye. The flesh will be unharmed and neither disease can be transmitted to humans.Photo's provided with permission from |
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Email the conservation director: vwagner@mnbf.org