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Fungal Diseases of Fish
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BRANCHIOMYCOSIS
Branchiomyces demigrans or "Gill Rot" is caused by the fungi Branchiomyces sanguinis and Branchiomyces demigrans. Branchiomycosis is a pervasive problem in Europe, but has been only occasionally reported by U.S. fish farms. Both species of fungi are found in fish suffering from an environmental stress, such as low pH (5.8 to 6.5), low dissolved oxygen, or a high algal bloom. Branchiomyces sp. grow at temperatures between 57 and 95F but grow best between 77 and 90F. The main sources of infection are the fungal spores carried in the water and detritus on pond bottoms.


Disease Signs
Branchiomyces sanguinis and B. demigrans infect the gill tissue of fish. Fish may appear lethargic and may be seen gulping air at the water surface (or piping). Gills appear striated or marbled with the pale areas representing infected and dying tissue. Gills should be examined under a microscope by a trained diagnostician for verification of the disease. Damaged gill tissue with fungal hyphae and spores will be present. As the tissue dies and falls off, the spores are released into the water and transmitted to other fish. High mortalities are often associated with this infection.


Management and Control
Avoidance is the best control for Branchiomycosis. Good management practices will create environmental conditions unacceptable for fungi growth. If the disease is present, do not transport the infected fish. Great care must be taken to prevent movement of the disease to noninfected areas. Formalin and copper sulfate have been used to help stop mortalities; however, all tanks, raceways, and aquaria must be disinfected and dried. Ponds should be dried and treated with quicklime (calcium oxide).


ICTHYOPHONUS DISEASE
Icthyophonus disease is caused by the fungus, Icthyophonus hoferi. It grows in fresh and saltwater, in wild and cultured fish, but is restricted to cool temperatures (36 to 68F). The disease is spread by fungal cysts which are released in the feces and by cannibalism of infected fish.


Disease Signs
Because the primary route of transmission is through the ingestion of infective spores, fish with a mild to moderate infection will show no external signs of the disease. In severe cases, the skin may have a "sandpaper texture" caused by infection under the skin and in muscle tissue. Some fish may show curvature of the spine. Internally, the organs may be swollen with white to gray-white sores.


Management and Control
There is no cure for fish with Icthyophonus hoferi; they will carry the infection for life. Prevention is the only control. To avoid introduction of infective spores, never feed raw fish or raw fish products to cultured fish. Cooking helps destroy the infective life stage. If Icthyophonus disease is identified by a trained diagnostician, it is important to remove and destroy any fish with the disease. Complete disinfection of tanks, raceways, or aquaria are encouraged. Ponds with dirt or gravel bottoms need months of drying to totally eliminate the fungus.


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