Columnaris Disease in Fish
(Flavobacterium columnare infection)
Columnaris disease is a serious bacterial infection in freshwater fish caused by Flavobacterium columnare. It is sometimes called “cotton wool disease” or “saddleback disease” due to its characteristic lesions. This bacterium thrives in warm, poor-quality water and can spread rapidly, causing high mortality if untreated.
Causative Agent
Bacterium: Flavobacterium columnare
Gram-negative, rod-shaped bacteria that target the skin, gills, and mouth of fish.
Can survive in water, substrate, and biofilms even without a host.
Transmission
Spread through direct fish-to-fish contact, contaminated water, nets, or equipment.
More common in tanks or ponds with high organic debris and warm temperatures (above 75°F / 24°C).
Signs & Symptoms
Skin lesions: White or gray patches that may look like cotton or fungus.
“Saddleback” appearance: Pale lesion across the back, near the dorsal fin.
Erosion or ulceration of the skin and fins.
Fraying fins with white edges.
Gill involvement: rapid breathing, gasping at the surface.
Lethargy and loss of appetite.
Diagnosis
A veterinarian may:
Examine skin or gill smears under a microscope (revealing characteristic columnar-shaped bacteria).
Culture bacteria for confirmation.
Treatment
Immediate water quality improvement: Partial water changes, removal of waste, increased aeration.
Antibacterial medications: Prescribed by a veterinarian; may be applied as baths, dips, or medicated feed.
Lowering water temperatures slightly (if species-appropriate) to slow bacterial growth.
Isolate the affected fish to reduce the spread.
Prevention
Maintain excellent water quality and filtration.
Avoid overcrowding and aggressive tankmates that cause injury.
Quarantine new fish for at least 4 weeks.
Disinfect nets, siphons, and equipment between uses.
Prognosis
Early treatment can save affected fish, but advanced cases—especially with gill involvement—often have a poor prognosis.
This disease can cause rapid, large-scale losses in warm, stressed systems.
Key Point:
Columnaris is often mistaken for fungal infections due to its cotton-like appearance, but it’s actually a bacterial disease that needs immediate veterinary-guided treatment.
Copyright © All Rights Reserved
