Columnaris

Complete guide to identification, timeline, and treatment

What is Columnaris?

Columnaris (Saddleback Disease or Cotton Mouth) is a bacterial infection caused by Flavobacterium columnare. Despite its fungal appearance, it is a gram-negative bacterium that thrives in warm, oxygen-poor water and spreads rapidly through fish populations.

Symptoms

White or grey patches on the back, head, or fins
Saddle-shaped lesion across the dorsal area
Frayed or eroding fins
White cottony tufts around the mouth
Ulcers on the body
Rapid breathing and lethargy

Causes

Poor water quality — high ammonia, nitrite, or nitrate
Low dissolved oxygen levels
High water temperature (above 77°F/25°C accelerates spread)
Stress from overcrowding or rough handling
Wounds or abrasions providing entry points

Columnaris Life Cycle and Timeline

Day 1–2
Bacteria enter through gills, mouth, or wounds. White or grey patches appear. Fish may show flashing or lethargy.
Day 3–5
Lesions expand rapidly. Saddle-shaped patches deepen. Fin erosion and ulceration become visible. Appetite declines sharply.
Day 6–10
Advanced ulceration and tissue necrosis. Secondary infections may develop. Mortality risk is high without treatment.
Day 11+
Without intervention, systemic infection causes death. Early treatment in the first 1–3 days is critical for survival.

Treatment Protocol

  • Immediately improve water quality — perform a 30–50% water change and increase aeration
  • Lower water temperature to 68–72°F (20–22°C) to slow bacterial growth
  • Quarantine affected fish to prevent spread to the rest of the tank
  • Treat with an antibiotic medication appropriate for gram-negative bacteria
  • Add aquarium salt (1 tbsp per 5 gallons) to reduce osmotic stress on affected fish
  • Continue treatment for the full course (7–10 days) even if symptoms improve early

Medication Options

  • Kanaplex (kanamycin) — highly effective antibiotic for gram-negative bacterial infections
  • Furan-2 (nitrofurazone) — broad-spectrum antibiotic; effective for Columnaris
  • Maracyn-2 (minocycline) — effective for internal and external bacterial infections
  • Triple Sulfa — sulfonamide antibiotic; good for surface lesions and fin erosion
  • Methylene Blue — supportive treatment for mild cases and secondary fungal infections
  • Avoid raising temperature during treatment — heat accelerates Columnaris progression significantly
Important

Columnaris is highly contagious and can spread through shared water, nets, and equipment. Disinfect all equipment between uses. Act within the first 24–48 hours for the best chance of recovery — delayed treatment significantly reduces survival rates.

Important Disclaimer

The information provided in this guide is for educational purposes only. Always consult with a qualified aquatic veterinarian or fish health specialist before administering any treatments. Proceed with treatments at your own risk. We are not responsible for any adverse outcomes.