Mouth Rot

Mouth Rot is a form of bacterial disease that eats away at the lips of koi and goldfish.  It will leave the fish with a deformed mouth if left untreated.

How to Recognize, Treat and Prevent Mouth Rot in Your Koi or Goldfish Pond

Mouth rot will appear often "for no reason".  You just notice a slight discoloration on the lips of the fish and, before you know it, the whole mouth is infected.  Sometimes it begins with an injury to the mouth.  We noticed this occurred more often in fish that were kept in tanks that were squared at the ends and not rounded.  We had one tank outfitted with netting used to separate koi into groups.  Unfortunately, the koi continually poked around the abrasive netting with their mouths looking for food and that caused injury that got infected and became mouth rot.

The area around the mouth becomes infected with bacteria and eventually the lips of the fish "rots" away.  We have had a few fish who have survived mouth rot but were unable to eat well because the disease left them scarred and deformed so that they could not scoop up the food like they normally do.   

Recognizing Mouth Rot

Mouth rot starts out as a slight discoloration in the area of the lips.  It becomes highly inflamed and the flesh begins rotting away.  Advanced cases, as shown above, will deform the lips and cause death.  The fish usually will die if the ulcer gets too far advanced.

The lips on this baby koi are infected with mouth rot.  It's still early in the disease and the prognosis is good that this koi will survive and not be disfigured.

Treating Mouth Rot

Bad (anaerobic) bacteria causes the infection.  It is naturally present in all bodies of water though some ponds are more ideal for breeding it.  It's not a bad idea to treat the whole pond with a bacterial treatment such as FuBa Fix if you suspect that your koi or goldfish are breaking down with mouth rot.  Remember not to allow any bacterial treatments to flow through your biological filter or you will end up without a functioning nitrifying cycle.  Bacterial treatments do not differentiate between good and bad bacteria.    

Simply sterilizing the pond of bacteria will not, as a rule, cure mouth rot.  It just helps hold off the bad bacteria.  For those fish that have the beginnings of mouth rot or in advanced cases a topical scrub or dip is recommended.  The best thing we've found for mouth rot is Tricide-Neo Ulcer Dip.  Unfortunately some fish are just too weak to withstand the harsh treatment.  For those fish we have Lil' Dab-a-do Ulcer Scrub.

Advanced koi hobbyists will often inject their prized koi with antibiotics.  These must be prescribed by a qualified veterinarian.  Often, though, we've found that Tricide-Neo and/or Lil' Dab-a-do will do the trick. 

You must be able to handle the fish every day for about a week so if you have a hospital tank it will make the treatments a whole lot easier on you and the fish.  You need not quarantine any fish with mouth rot (unless you have the availability of a hospital tank) because unless a fish's immunity is weak (or there are other stress factors going on such as water parameters are bad or parasites are present) he shouldn't break down with mouth rot by simply swimming with an infected fish.

If the fish can eat, start feeding your fish with triple antibiotic food and only the medicated food for about 2 weeks.  Then stop.  This will insure that you are attacking the infection from inside as well as the outside of the fish.

Emergency Procedures

1. Begin treatment immediately on any fish that shows infection around the mouth with either a dip (Tricide-Neo) or Lil' Dab-a-Do Ulcer Scrub -- (or if you are able, a series of injections - see your veterinarian for assistance).
2. Begin feeding with triple antibiotic food.

What to Expect Next

Mouth rot often leaves the lips of the fish deformed and can impede on the fish's ability to eat.  You may have to use smaller pellets for koi or goldfish who cannot open their mouths properly. 

Preventing Mouth Rot

Sometimes even the best of us have problems with mouth rot no matter how diligent we are about keeping the pond healthy.  Overcrowding is always a problem (even in our own personal pond) because we all tend to have too many koi and goldfish and mouth rot can occur simply because of that.  Keeping the pond clean is a must for koi ponds.  Not lining the pond with rock will prevent junk from settling in between the crevices and becoming a breeding ground for anaerobic bacteria.  Keeping the fish healthy is the trick to fighting mouth rot.  As a precaution in spring we like to feed our fish nothing but triple antibiotic food for two weeks. 

Another way to prevent mouth rot is to make sure their are no sharp edges or corners that can cause injury to the mouth.  Keep them away from abrasive materials such as the netting we used.

More Information About Mouth Rot

• How to Prevent Spring Disease Outbreaks in Koi & Goldfish
• Battle of the Bacteria
• Tricide-Neo Antibiotic Dip for Ulcer Disease in Koi & Goldfish

Items You Might Need:

Tricide-Neo

Lil' Dab-a-Do

FuBa Fix

Triple Antibiotic Food

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