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Tropical Fish Diseases - Cotton Mouth Disease

Updated on July 12, 2011

Of all the tropical fish diseases your fish can get, cotton mouth is one of the worst. Why? It's simple. This disease is extremely contagious. If you don’t catch it in time and your fish are untreated, they die within 48 to 72 hours. The sick fish can also pass cotton mouth on to the rest of the fish in your aquarium, infecting the entire tank of fish.

What Causes Cotton Mouth?

This tropical fish disease is a bacterial infection that is pretty common. Some tropical fish hobbyist refer to it as Columnaris and happens from tank overcrowding and low levels of oxygen levels in the tank. You can also bring in this bacterial infection by buying sick fish. The fish get the bacteria by taking it into their mouths, gills or through any small cuts or wounds that they may have.

What are the Symptoms of Cotton Mouth?

The first symptom of Cotton Mouth disease is the frayed and ragged fins on your fish. Next, within 24 to 48 hours, you'll begin to notice sores are your fish that appear to be mold. The sores can be pale and barely noticeable, or they can be the "saddleback" lesion that goes from the dorsal fin down each side of the fish giving the appearance of a sadle.

Tropical Fish Diseases
Tropical Fish Diseases | Source

After these signs appear, you'll notice the fish's mouth looks like it is being eaten away and the gills begin to change color. The fish then begins having problems with their gills and start having trouble breathing. The fish can die within 48 to 72 hours after you notice these signs. 

What is the Treatment of Cotton Mouth? 

You need to begin treatment immediately if you think your fish are suffering from this tropical fish disease. First, isolate the fish from the rest of the tank so the disease can't spread. Next, give the fish food that has oxytetracycline in it. Oxytetracycline is an antibiotic that can kill the bacteria.

Stop using carbon filtration during the treatment and add aquarium salt to improve the fish's gill function. Increase the water agitation and aeration to help dissolve oxygen levels in the tank. This makes it easier for the fish to breath. After you’ve isolated and treated the infected fish, you need to thoroughly clean the tank you removed him from. Change the water and vacuum the gravel. 

Because cotton mouth is highly contagious, you need to know and recognize these signs and symptoms. This is one of the fastest spreading tropical fish diseases your fish can possibly get. If left untreated, it can potentially kill every fish you have.


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    • profile image


      6 years ago

      thank you helped me out a lot I just hope it helps my fish

    • mackyi profile image

      I.W. McFarlane 

      8 years ago from Philadelphia

      This is an informative hub for all fish enthusiast, including myself. Looking forward to read future hubs on fish disease or fish care.

    • Debhsmomof4 profile imageAUTHOR


      8 years ago from New York, New York

      Thanks! Glad you liked it.

    • coolbreeze profile image

      Rik Rodriguez 

      8 years ago from Hawaii

      Nice Hub I am going to share it with my friends on Facebook!


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