How to Prevent Columnaris Disease in Your Aquarium Fish

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If you notice fluffy, white spots on one or more of your fish, then at first you can assume that some type of fungus is causing the problem. However, this is not necessarily the case. Your fish could have a disease called columnaris.

What is Columnaris? What causes the disease and will your fish die?

This guide will tell you everything you need to know about Columnaris, including how to identify, treat, and prevent the disease.

What is Columnaris?

Many fish owners mistake Columnaris for a fungal disease because of the mold-like lesions caused by the disease. However, columnaris is a common bacterial infection that can manifest itself externally or internally, and the disease can be acute or chronic in nature.

The bacteria, Flavobacterium columnare, cause the condition. The bacteria have a columnar shape and it is this characteristic that gives the disease its common name. You can also see the disease known as cotton wool disease, guppy disease, saddle back disease, or cotton mouth disease.

Columnaris can attack all freshwater fish species, although catfish and livebearers appear to be particularly susceptible. Although the condition looks a bit alarming, in general, the disease can be treated successfully with antibiotics, provided that it is detected early and the underlying causes are corrected.

What are the symptoms of columnaris in aquarium fish?

Columnaris can present externally or internally.

External Columnaris Symptoms

Columnaris infections generally appear externally as gray or white spots or spots on the fish’s head and around the gills or fins. At first glance, the lesions look like a pale spot that lacks the shiny, light color of the rest of the fish’s body.

As the lesion develops, the area around it may become red and the lesion itself may turn brown or yellow. The lesions on the fish’s back often spread over the sides of the creature, giving the impression that the fish is wearing a saddle. Hence, the disease is often referred to as saddle back disease. Lesions around the fish’s mouth can look like mold or cotton, and eventually the animal’s entire mouth can be eaten away completely.

As the infection progresses, the fins begin to erode and look irregular. The fish’s gills can also be affected. When the bacteria enter the gills, the filaments fall apart, which allows the fish to breathe quickly when they have difficulty taking in oxygen.

Internal lesions

Sometimes the Columnaris infection affects the fish internally and there are no external symptoms, making it extremely difficult to diagnose. In these cases, the fish usually dies before effective treatment can be given.

In cases of chronic disease, the lesions spread and develop very slowly. It often takes many days to kill the fish. When the disease is more acute, the lesions spread rapidly, sometimes resulting in mass fish being killed within a few hours.

When the water temperature is increased, the spread and progression of Columnaris infection will accelerate. Unfortunately, lowering the water temperature will not help stop the disease from progressing or affect its possible outcome.

Sick fish generally isolate themselves from their roommates and stop eating.

What causes columnaris in fish?

There is no single cause of Columnaris disease in fish. The condition is usually caused by a number of factors, many of which are easily preventable with proper aquarium management and housing. Here are the most common causes of columnaris in aquarium fish.

Aquarium environment

The main cause of Columnaris infection outbreaks are poor water conditions. Fish kept in unsanitary water that is high in ammonia, nitrites and nitrates can become stressed, affect the animals’ immune systems and make them vulnerable to attack by bacteria and parasites.

Although many potentially harmful bacteria are naturally found in ponds, rivers, and other bodies of water, their concentrations are low and water quality is generally balanced and kept clean by rainfall and natural currents. In an aquarium, however, the environment is enclosed. So if you do not properly clean and maintain the tank and filter systems, the level of pollutants and waste in the water will quickly rise to dangerous levels.

Overstocking makes conditions worse, as does overfeeding. Both scenarios, in combination with infrequent partial water changes and insufficient maintenance of the filter media, can provide the perfect environment for bacteria such as columnaris to multiply.

Bad diet and bad diet

Properly feeding your fish and providing adequate nutrition for the species is critical to the health of your cattle. If the fish are not given high quality food that meets their needs, they will quickly become stressed and vulnerable to attack by the Columnaris bacteria.

Wrong water parameters

If you keep fish in water that is too warm, too cool, too hard or too soft, too alkaline or too acidic, they can be weakened and the creatures can be attacked by bacteria.

So invest in a reliable aquarium thermometer and make sure to use an aquarium test kit to monitor the pH and nitrogen compounds in the water every week.

Cross contamination

Columnaris is highly contagious and can be distributed between tanks through contaminated containers, nets, and even food.

So take great care to keep the equipment clean, and ideally use a separate kit for each of your tanks to avoid cross-contamination.

How to treat columnaris

The good news is that Columnaris is treatable provided you catch it early enough.

External columnaris infections can be treated with antibiotics, certain chemicals, or both. You can use acriflavin, copper sulfate, terramycin, and furan, all of which are effective in treating the bacteria.

Terramycin is extremely effective when used as a bath to treat external infections. You can also lace foods with the drug to treat internal cases of the disease.

You can reduce the osmotic stress on your fish caused by the damage to the fish’s skin from the lesions by treating the water with aquarium salt. Use one to three teaspoons of aquarium salt per gallon of water for best results. Salt is particularly effective in treating livebearers. However, be careful when using salt in a tank that contains catfish, as these can be very sensitive to it.

How to prevent columnaris

Columnaris is easily preventable.

The bacteria live on organic waste. By keeping the aquarium clean, doing partial water changes weekly, and vacuuming the substrate thoroughly to remove fish waste and uneaten food, you can prevent an outbreak.

As mentioned earlier, your fish should be given appropriate nutrition for the species to keep them healthy and prevent stress.

All new fish should be placed in a quarantine tank for a few weeks before adding them to your main display setup. We recommend that you fill your fish with a net in your display tank rather than directing potentially contaminated water into the clean aquarium. If you discover a fish in your main tank that appears sick, remove it immediately and place it in quarantine to prevent the disease from spreading to other fish in the tank.

When treating an outbreak of any disease in your tank, always disinfect all aquarium equipment after each use. A commercial treatment of benzalkonium chloride solution (Net Soak or Net Dip) should be used, or you can soak items in a 3% hydrogen peroxide solution if you prefer.

Final thoughts

Columnaris is a bacterial infection that can affect all types of aquarium fish, especially livebearers and catfish.

The disease is often mistaken for fungus because of the cotton stains that appear over the fish’s body and head. However, the condition is caused by a bacterium.

Although the disease is treatable if caught early, you can easily prevent columnaris outbreaks by keeping your aquarium clean, maintaining your filtration systems, properly feeding your fish, and monitoring water parameters to make sure they are suitable for the species of fish you use have in your collection.

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