Columnaris

Columnaris is a common and highly contagious bacterial infection in freshwater fish caused by Flavobacterium columnare. Despite its common name 'mouth fungus,' it is bacterial, not fungal. The disease can affect the skin, fins, gills, and mouth, progressing rapidly in warm water conditions. It is one of the leading causes of fish mortality in aquaculture and aquariums.

Symptoms & Signs

• White or grayish patches on body, fins, or mouth
• Frayed fins with white edges
• Saddleback lesion (pale band behind dorsal fin)
• Gill necrosis
• Rapid breathing
• Lethargy
• Loss of appetite
• Mouth erosion

Causes & Risk Factors

Caused by Flavobacterium columnare, a gram-negative rod bacterium. The organism is ubiquitous in freshwater environments. Outbreaks are triggered by stress, high water temperatures (>20C/68F), poor water quality, overcrowding, and physical damage to skin or gills. The bacteria form biofilms on fish tissue.

Diagnosis

Wet mount microscopy of skin scrapes showing long, thin rod-shaped bacteria in 'haystack' formations. Characteristic yellow-pigmented colonies on selective media. PCR for definitive identification. Clinical presentation with saddleback lesions is highly suggestive.

Treatment

External: potassium permanganate dips, copper sulfate, salt baths. Systemic: medicated food with antibiotics (florfenicol, oxytetracycline). Improve water quality and reduce temperature if possible. Treat early as progression is rapid.

Prevention

Maintain excellent water quality. Avoid overcrowding. Minimize handling stress. Quarantine new fish. Keep water temperature stable. Avoid temperature spikes above 68F/20C in susceptible species. Adequate nutrition to maintain immune function.

Prognosis

Good if caught early and treated aggressively. Gill involvement carries worse prognosis. Chronic columnaris can be difficult to eliminate from a system. Prevention through good husbandry is essential.

Affected Breeds (5)

Related Conditions

• Fin Rot
• Ich (White Spot Disease)
• Bacterial Infections