Columnaris

Columnaris (also referred to as cottonmouth) is a symptom of disease in fish which results from an infection caused by the Gram-negative, aerobic, rod-shaped bacterium Flavobacterium columnare. It was previously known as Bacillus columnaris, Chondrococcus columnaris, Cytophaga columnaris and Flexibacter columnaris. The bacteria are ubiquitous in fresh water, and cultured fish reared in ponds or raceways are the primary concern – with disease most prevalent in air temperatures above 12–14°C. It is often mistaken for a fungal infection. The disease is highly contagious and the outcome is often fatal. It is not zoonotic.