Flexibacter Columnaris is the bacteria that cause this disease in the fish. These are gram negative bacteria. The other names for this infection are Flexibacter, Mouth Fungus, Cotton-Wool, Cotton-Mouth, and Columnaris. The bacteria is columnar shaped and hence this name for this disease. The fishes like cat fish and other live bearing fishes are those that are mostly affected by Flexibacter Columnaris. Often this infection is mistaken for a fungal infection. This bacterium is found more commonly in all aquariums. However the infection is through only on the fishes that are stressed much due to environment or other health conditions. Improper handling of the fish, inadequate food, and bad quality of water are the causes for the stress in fish. These conditions will work in favor of the Flexibacter Columnaris to infect the fish.
The bacterial enters the fish through the gills, mouth, or through the already existing wounds on the skin of the fish. If the fish is already infected with some other disease that affects the skin condition like velvet disease, it is easy for the bacteria to get in to the fish. This infection is also contagious. Hence it is better to keep the accessories related to the aquarium very clean from infections. A net that is already infected by Flexibacter Columnaris if used in an aquarium it would spread the bacteria to that aquarium too. The infection caused by these bacteria could be acute or chronic. In acute cases disease progresses faster and in chronic cases it takes a few days to affect. Acute cases of infections spread to other fishes faster and eventually all of them would be dead in a few hours too. If the temperature of the water is high then the progression of the disease is quite faster.
Some of the symptoms that you can notice with this infection are cotton like growth near the mouth of the fish. You can also see white spots on the fins, scales, and the mouth. In some cases the fins might also disintegrate at the edges. A saddle like lesion is seen on the dorsal fin. This gives way to other fungal infections. Breathing becomes difficult which is evident with faster flapping of the gills. Although the infection can be either internal or external, most of the infections are external only. Any area that is not shiny on the skin is prone to the infections mostly. The lesions progress from yellow color to brown color to red as the infection reaches the advanced stages.
The gravel in the aquarium has to be vacuumed properly and the water changed in the aquarium. You can also add aquarium salt to the water, but make sure there are not cat fishes in it as the salt might affect it. Copper sulphate or any antibiotic treatment is used to fight this infection. Carbon infiltration has to be stopped during this treatment. Antibiotics like Terramycin and Acriflavine can be used in the treatment. Once the salt is added to the water you can see improvement in the gill function. Quarantine the new fishes that are to be added for two weeks to avoid this infection. Always maintain good quality of water and give a balanced food to the fishes to prevent this disease.