Columnaris betta

Columnaris Betta: ID, Treat, and Prevent

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First and foremost, columnaris is primarily identified by its tell-tale cottonmouth symptom. It is caused by the bacteria Flavobacterium columnare. If you believe your fish may have such an infection, it is important to take immediate action to help prevent mortalities. Read on for more information regarding this infection and seek assistance from a professional who specializes in tropical fish immediately.

Columnaris Overview

Columnaris is known by many different names. Cotton-Wool, Cotton-Mouth, Flexibacter, Mouth Fungus, Mouth-Rot, and Saddle Back. Columnaris can be external or internal and may follow a chronic or acute course.

Fish with chronic conditions tend to progress slowly, taking many days before eventually ending in fish death. In the more acute cases, the lesions spread quickly and can wipe out entire populations of fish within hours. Warmer water temperatures will accelerate the progression of the disease. Unfortunately, lowering the temperature will not affect the outcome. Most species of fish become susceptible to columnaris following some type of environmental stress.

What to Look For

Early on, you can spot fraying on the fins as a sign of bacterial infection. Soon after this fraying stage, ulcerations will begin to appear on the fish’s skin. You may also see signs of lethargy, color loss, redness/irritation, appetite loss, and more. The ulcerations typically appear within 24 to 48 hours of infection, and fatality soon follows (at 48-72 hours). This is why it is imperative to take immediate action to seek treatment.

Here are a few key things to look for:

  • White spots on the mouth, edges of scales, and fins
  • Cottony growth that eats away at the mouth
  • Fins disintegration, beginning at the edges
  • ‘Saddleback’ lesion near the dorsal fin
  • Rapid gilling in cases of gill infection

Infection Progression

Most Columnaris infections are external and will show up first as white or grayish spots on or around the head and around the fins or gills. In the beginning, the lesions are shallow and appear as a paler area that lacks the shiny normal appearance you see on the rest of the fish. As the lesions progress, they may become yellowish or brownish in color and the area around it may appear red.

The bacteria also attach to the gill surface, grow in spreading patches, and eventually cover the filaments of each gill, and the result is cell death. Then, the protein and cartilage-degrading enzymes of the bacteria destroy portions of the gills. Mucus often also accumulates on the gills, head, and dorsal regions.

As the bacteria advances, the round or oval lesions develop an open ulcer in the center. A  pale white band encircling the body is a characteristic lesion pattern giving rise to the term saddleback condition. A yellowish-brow ulcer appears in the center of the “saddle” as the infection progresses.

In addition, mucus-like growth of columnaris bacteria the is also yellowish brown will sometimes develop inside the fish’s mouth. On the mouth, the lesions may look moldy or cottony, and the mouth will eventually become eaten away. The brownish coloration is attributed to mud and detritus particles trapped in the slime/mucus produced by the bacteria.

As the bacteria invade the gills, the filaments will disintegrate, resulting in the onset of rapid breathing or gasping in the fish due to lack of oxygen. Fish will breathe rapidly and laboriously as a sign of gill damage.

Less commonly, the infection will take an internal course which often displays no external symptoms. In these cases, only a necropsy and cultures will point to the true cause of death.

Getting it and Getting Rid of it

Columnaris bacteria are more apt to infect fish that have been stressed by conditions such as poor water quality, inadequate diet, or stress from handling and shipping. The bacteria gain entrance to fish through the gills, mouth, or any small wounds on the skin. Columnaris is highly contagious, often spreading via nets, tanks, and even food. There are many reasons to use sterile techniques to avoid contamination, and this is one of the big ones.

Once discovered in your fish room, treatment of any and all other tanks and paraphernalia is a good precaution, and becomes mandatory if they share a common filtration system.


As we mentioned, Columnaris bacteria usually gains access to your fish’s system through the gills, mouth, or small scratches on its skin. Columnaris bacteria probably occur in most, if not all, aquaculture environments. The bacteria can cause disease under normal culture conditions, but the infection is more likely to take hold in stressed fish.

Stressful conditions favoring columnaris disease include low oxygen, high ammonia, high nitrite, high water temperatures, rough handling, mechanical injury, and crowding. Columnaris occurs frequently in fish raised intensively in cages and in closed recirculating systems and is attributed to crowding and cage abrasions.

Once established, the infection can spread quickly and cause high mortality rates. While stressful conditions can contribute to columnaris infections, the presence of columnaris may also lead to secondary infection or other diseases. Columnaris often proceeds Winter saprolegniosis (aka winter fungus or winter kill).


As Flavobacterium columnare is Gram-negative, you can treat your betta with a combination of the antibiotics furan-2 and kanamycin. Medicated food containing oxytetracycline is also an effective treatment for internal infections, but resistance is emerging. You may apply potassium permanganate, copper sulfate, and hydrogen peroxide externally to adult fish and fry, but be aware that these can be toxic in high concentrations. Vaccines can also help in the face of an outbreak or to prevent disease occurrence.


Prevention is just as important as treatment. Here are a few steps to take to help prevent Columnaris outbreaks in the first place:

  • Quarantine new fish for two weeks
  • Maintain high water quality
  • Provide fish with a nutritionally balanced diet
  • Medicate fish prophylactically before moving them
  • Disinfect nets and other equipment before using

Because the bacteria thrive on organic wastes, the potential for columnaris outbreaks can be controlled by regular water changes and tank maintenance, including vacuuming of the gravel. Proper diet and maintaining good water quality, in general, will reduce stress and chances of infection. Placing new fish, and promptly moving any sick fish to a quarantine tank will help prevent the introduction and spread of the disease.

To avoid spreading the disease to other tanks, you should disinfect nets, specimen containers, and other aquarium equipment before each use. Using small quantities of aquarium salt regularly can help to prevent disease in livebearer aquariums. When shipping or moving fish, the stress leaves them open to contracting a disease. To give them a better chance of remaining healthy, you may give them preventative antibiotic treatment or medicated food.

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