Columnaris
Flavobacterium columnare
High severity ⚠️ Contagious
A fast-moving bacterial infection often mistaken for a fungus, forming white cottony patches.
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Symptoms
White/grey cottony patches, 'saddleback' lesions across the back, frayed mouth and fins, rapid breathing.
Causes
A bacterium that thrives in warm, dirty, low-oxygen water and attacks stressed or injured fish.
Treatment
Lower the temperature slightly (warmth accelerates it), improve oxygenation and water quality, and treat with an antibacterial effective against gram-negative bacteria. Acts quickly so treat immediately.
Prevention
Avoid overcrowding and warm stagnant water; keep oxygen high and water clean.
FAQ
Is columnaris a fungus?
No — despite its cottony look it is bacterial, so antifungal treatments won't work. Use an antibacterial.
How fast does columnaris kill?
Aggressive strains can kill within 24-72 hours, so immediate treatment is critical.
This information is general guidance, not veterinary advice. Consult an aquatic vet for serious cases.