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Columnaris is a symptom of disease in fish which results from an infection caused by the bacteria Flavobacterium columnare. The disease is highly contagious and the outcome is often fatal.


The bacterium usually enters fish through gills, mouth, or small wounds, and is prevalent where high bio-load exists, or where conditions may be stressful due to overcrowding or low dissolved oxygen levels in the water column. The bacteria can persist in water for up to 32 days when the hardness is 50ppm or more[1].


An infection will usually first manifest in fish by causing frayed and ragged fins. This is followed by the appearance of ulcerations on the skin, and subsequent epidermal loss, identifiable as white or cloudy fungus-like patches. Gills will change colour, either becoming light or dark brown, and may also manifest necrosis. Fish will breathe rapidly and laboriously as a sign of gill damage.


Ulcerations develop within 24 to 48 hours. Fatality occurs between 48 to 72 hours if no treatment is pursued.


Attempts to feed infected fish with medicated food containing oxytetracycline should be made. Due to the nature of infection, however, fish may no longer be eating. In this case application of an antibiotic is necessary. Sulfate based drug combinations such as TMP Sulfa, Sulfa 4 TMP, or Triple Sulfa, are said to combat the infection. Erythromycin (Maracyn), nitrofurazone, nifurpirinol, acriflavine, chloramphenicol or tetracycline are also suitable treatments. Increased aeration and water agitation will improve dissolved oxygen levels which may assist fish suffering from gill damage.


  1. Aukes, G., Fish disease articles: Columnaris disease, [Retrieved 25th July 2007]

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