Columnaris (Cotton Wool Disease)
Skin and gill bacterial infection in warm freshwater fish — fast onset above 25°C.
Clinical signs
- Grey-white, slightly raised patches on the skin — often forming a 'saddleback' lesion across the dorsal fin base
- Frayed, ragged fins (fin rot) with white margins
- Pale, swollen, mucus-coated gills (gill rot) — fish gasp at the surface
- Mouth lesions and erosion around the lips ('cotton-mouth')
- Lethargy, schooling near aerators, refusal of feed
- Acute mortality 30–90% in 48–72 hours at >28°C; chronic form spreads over 1–2 weeks at cooler temperatures
Transmission
- Waterborne — Flavobacterium columnare is endemic in most warm freshwater systems
- Disease triggered by stress: high temperature (>25°C), high stocking density, low DO, ammonia spikes, handling injuries
- Direct contact between fish accelerates spread within a pond
- Mechanical via shared nets, grading boards and transport tanks
- Virulence rises sharply above 28°C — a 3°C temperature jump can convert latent carriage into an outbreak in 24 hours
Diagnosis
- Field: saddleback lesion + frayed fins + warm water = high-probability columnaris
- Microscopy of a skin or gill scrape — long, slender rods that form characteristic 'haystack' columns; gliding motility on the slide
- Selective culture on Cytophaga agar — yellow, rhizoid colonies
- Differentiate from Saprolegnia (true cotton-wool tufts, fungal hyphae under microscopy) and Ich (raised round white spots)
- PCR for the 16S rRNA gene confirms in ambiguous cases
Treatment & emergency response
- Lower pond temperature 2–3°C where possible (deepen water, increase shade, more aeration)
- Salt bath at 0.3% (3 g/L) sustained for 7 days — supports osmoregulation in damaged fish and slows bacterial growth
- Potassium permanganate (KMnO₄) bath at 2 mg/L for a single treatment (consult local regulations; the active dose depends on organic load)
- Reduce feeding by 50% for 5 days to lower organic load and ammonia
- Maintain DO above 6 mg/L — damaged gills require more oxygen
- Increase water exchange (10–15% daily) where biosecurity allows
- Antibiotics (oxytetracycline, florfenicol) only with a vet prescription, lab sensitivity report, and strict withdrawal-period compliance
Prevention
- Maintain stocking density within species norms — tilapia outbreaks cluster above 25 fish/m³ in tanks and 5 t/ha in earthen ponds without aeration
- Avoid water temperatures above 28°C — deepen ponds, add shade nets, run aeration at night
- Keep ammonia below 0.5 mg/L and DO above 5 mg/L at all times
- Handle fish only in cool early-morning hours; never grade or net during midday heat
- Quarantine new fish for 14–21 days; pre-treat with a 3 g/L salt bath before stocking
- Sanitise transport tanks and grading equipment between batches (KMnO₄ 10 mg/L)
- Vaccinate tilapia broodstock against columnaris where commercially available (Asia, Latin America)
Biosecurity checklist
- Foot baths and equipment disinfection at every pond entry
- Dedicated nets per pond; colour-code to prevent cross-use
- Daily DO, ammonia and temperature log; spikes trigger pre-emptive salt treatment
- Pre-stocking salt dip (3 g/L for 15 minutes) for all incoming fingerlings
- Drain and sun-dry empty ponds for 7+ days between batches
- Train workers to distinguish saddleback (columnaris) from cotton-wool tufts (saprolegniasis)
- No grading or transport when forecast water temperature exceeds 28°C for 48 hours
Regional prevalence
See where Columnaris is being reported right now across India and Southeast Asia, with weekly trend lines and per-district drilldowns.
Open the heatmap →Frequently asked questions
What is columnaris disease in fish?
Columnaris is a bacterial infection caused by Flavobacterium columnare. It primarily attacks the skin, fins and gills of freshwater fish — most aggressively in tilapia, catfish and Indian major carps. The bacterium is endemic in most warm freshwater systems; disease only erupts when fish are stressed by heat, crowding, low DO or handling.
What causes columnaris outbreaks in tilapia ponds?
Three stressors trigger almost every outbreak: water temperature above 28°C, stocking density at or above species limits, and handling injuries from grading or transport. The bacterium is always present in the water — disease begins only when fish immunity drops. Outbreaks above 30°C can move from first symptoms to 70%+ mortality in 48 hours.
How do you treat columnaris in a pond?
Drop pond temperature 2–3°C where possible (deepen water, add shade, increase aeration), apply a 0.3% salt bath sustained for 7 days, cut feed by 50% to reduce organic load, and maintain DO above 6 mg/L. Potassium permanganate at 2 mg/L can be added as a single bath for severe cases. Antibiotics (oxytetracycline, florfenicol) require a vet prescription and strict withdrawal compliance.
Is columnaris the same as fin rot?
Columnaris is a common cause of fin rot, but not the only one. Fin rot is a symptom (frayed, eroded fin margins) that can be caused by columnaris, Aeromonas, Pseudomonas or chronic ammonia stress. A skin scrape under the microscope showing long gliding rods forming haystack columns confirms columnaris specifically.
Can columnaris affect humans?
No. Flavobacterium columnare is a fish-specific pathogen and does not cause disease in humans. Properly handled fish are safe to eat after the standard withdrawal period for any antibiotic used; salt and KMnO₄ treatments do not require a withdrawal period.
How is columnaris different from saprolegniasis?
Columnaris produces flat, grey-white patches with frayed edges — it does not form raised tufts. Saprolegniasis produces true cotton-wool growths that you can lift off the fish with a needle. Under the microscope, columnaris shows long gliding bacterial rods; saprolegniasis shows branching fungal hyphae. Columnaris also tends to attack the gills heavily, while saprolegnia rarely does.
Catch Columnaris before it costs a cycle
CAMARON's Disease Vision module flags Columnaris from a single farm photo, ties findings to the regional heatmap, and walks you through the protocol.