This disease is a common bacterial infection that is also known as Columnaris and can occur from overcrowding and low oxygen levels in the tank or being brought in when a new fish is introduced into your aquarium. The bacteria enter the fish through their mouth and gills, or through any small wounds that the fish may have.

Symptoms

The symptoms of Cotton Mouth disease are first seen in frayed and ragged fins shortly followed within 24 to 48 hours by mold-like lesions or sores. The sores can be obvious as with a ‘saddleback’ lesion, which extends from the dorsal fin down each side on the fish like a saddle, or they can appear to be only a ‘paler’ area or not as shiny as the rest of the fish. After these first signs, the mouth will become eaten away and the gills will change color to either a light or dark brown. As signs of gill damage set in, the fish will begin to breath rapidly and laboriously. Within 48 to 72 hours after these signs appear, the fish can die.

Treatment

If you have diagnosed your fish as having Cotton Mouth disease, you need to begin immediate treatment. Your first step is to isolate the sick fish from the healthy fish and give it medicated fish food that contains oxytetracycline, an antibiotic. If the fish isn’t eating, you will need to apply a topical antibiotic such as TMP Sulfa, Sulfa 4 TMP, or Triple Sulfa made for this disease.

Next, change the water in the tank and vacuum the gravel. Add aquarium salt to improve gill function and discontinue carbon filtration during the treatment. Increase aeration and water agitation to dissolve oxygen levels. This will help the fish that are having trouble breathing due to gill damage.

It is important to recognize the symptoms of Cotton Mouth disease in your fish because it is highly contagious. Because this disease spreads rapidly, it has the potential to infect every fish in the tank, and destroy all of your fish. Keep your tank well aerated, clean, and don’t overcrowd it. These precautions will help prevent this fatal disease.