Mouth Rot

Mouth rot is most commonly associated to be a disease in the aquarium and pond world, however in reality it is more of a symptom showing poor signs of various things relating to the water quality. Mouth rot is actually a bacterial infection that only will effect the mouth of the fish it infects, creating a rotting effecting when visible. Although this is a problem that is seen more when fish are housed outside of their natural environment, it can be and is seen within wild populations of fish in their natural waters.


Mouth rot is a symptom that can be noticed almost right away due to the mouth being one of most looked at parts of any fish. The mouth can range from a variety of designs, however they will all share the same signs if the fish is infected with this bacteria. Depending on the fish their mouth may appear to be falling off, mouth will start to appear red, and at the worse case the whole mouth will be missing. Due to the way that some decorations are made, many owners will start to blame the fact that the fish may have hit the decoration wrong and that is why the fish is missing it's mouth (or it's damaged). When you first spot any fish that has any damage to it's mouth, we suggest that you make sure that no decorations inside could cause any damage to any fish's mouth and that there isn't any fish that are attacking it during the night or when you aren't looking at the tank. If theses steps are already done and it is neither of these being the cause, then the fish might be infected by this bacteria.


Mouth rot can be caused by a variety of factors that can either be related to the water parameters, to others that might be caused by nature itself. Since mouth rot is a bacterial infection and not a disease, anytime that a fish has it's mouth attacked or pulled which causes the damaged mouth to become infected. The most common cause will be housing two different species that do not mix (examples would be having a fast moving fish which are common nippers with slow fish). May times this cause is dismissed since the fish store states that they are peaceful towards other tank mates, but like anything bred in the wild or in the aquarium we need to keep in mind that every fish will have it's own temperament. As always, we suggest that you read various articles on the species of fish that you are wanting to keep in order to make sure that they can co-exist peacefully with any other tank mates you plan to add. Other times fish may start to nip at each other's mouth if the aquarium or pond is overcrowding leading to the strongest fish trying to eliminate the weaker fish. The same can be said if a weekly feeding schedule is not maintained, as the more powerful or dominate fish that are hungry will try to eat the other peaceful fish that may be the same size or even smaller.

Water parameters can be another cause for mouth rot to start to develop on various fish. If the water parameters are high in toxins (ammonia, nitrites, and/or nitrates) and water changes are not done to remove such toxins, the fish can get infected with this bacteria and start to develop mouth rot. Although this is less common, making sure to always remove any decaying matter such as excess food, dead plant matter, dead fish or invertebrates, and most importantly having control over the nitrogen cycle will make sure that the water parameters never get out of control.

Treatment and Medications

Treatment of mouth rot can depend mostly on how badly the fish's mouth is, if they are infected, or if there are just a few rips here and there. If the fish's mouth are only slightly damaged then doing a big water change of around 50% and maintaining the water parameters throughout can lead to the fish recovering on it's own. If the fish's mouth is badly damaged, infected, or worse we suggest using medicine to treat mouth rot. Medicines that work the best include, but are not limited to Maracyn, MelaFix, PrimaFix, Methylene Blue, and other anti-bacterial medicines will work the best. When using any medicine, it is recommended to remove any carbon from the filter media and to also turn off any UV sterilizers or protein skimmers during usage. It is recommended to remove all decorations in the tank before using methylene blue as it can stain them a slight shade of blue throughout the treatment and if you have any sensitive species within your aquarium please use these medicines at roughly half strength. We recommend following the product's instructions on the bottle when using either of these products.


Due to the way that this disease spreads and effects the inhabitants, the best prevention methods are to always make sure that you quarantine anything that you place inside of your water (this includes any plants, inhabitants, decorations, and more). Thus, when you do let them adjust to your water and you truly see how they are acting, eating and if they have any symptoms or signs, we will either start to get a better understanding if they are infected, or learn about what possible other diseases they might have.