Corydoras Mouth Rot :(

Ridge Chambers


30 gallon tank
Has been running for 6 months
Filter: just upgraded from aquatech 20-40 to aquaclear 70
Heated to 76°F
Stock - 4 black schultzI / Venezuelan black corydoras
- 3 sterbaI corydoras

50% WC once a week
I Treat tap water with prime
I usually just hover the gravel vac above the sand

*Parameters - Very Important
I did cycle the tank before adding fish
I test with API freshwater test kit

Ammonia: 0
Nitrite: 0
Nitrate: 0-5
pH: 7.4 - 7.6

I feed once a day.
I feed one cube for 7 Cory cats.
I feed mostly Omega one frozen food. Once a week I feed a dry food.

Illness & Symptoms
I have had the 2 affected fish for about 3 months.
I noticed the infection 2 and a half weeks ago.
The barbels are gone and the area surrounding the mouth is swollen and white.
I started daily 50% WCs and paraguard on day one - day 7. Added carbon and continued daily WCs of 50%
When I first got the fish I hadn't properly seeded the sponge filter that I was using for the qt tank and unfortunately an ammonia spike killed all but 2 of the young corydoras.
They are still eating and are still quite active. They seem healthy besides the rotting mouth.

Explain your emergency situation in detail.
I can't tell if the other fish are starting to show symptoms or not. They naturally have a lighter colored mouth and barbels.
I live in Canada, where it has become extremely difficult to find fish meds. Even if the active ingredients haven't been restricted.

I have enough maracyn 2 for a full round
In the display tank.
I have enough maracyn for one full round of maracyn 1 and 2 in a QT tank.
I have enough bifuran for 2 full rounds in a QT tank.

I'm thinking I will move the fish that are clearly affected to a 10 g QT and start treating with bifuran. I should also be able to get kanaplex + furan and sulfa based meds on eBay from the states. They shouldn't be seized at the border, hopefully. I will also give the local fish stores a call to ask what they still stock.

If anyone has a better plan or any kind of helpful input I am all ears.


Sounds like you're on the right track with getting the Cories medicated.

Just be careful as they are scaleless fish, so observe them for any possible stress during the treatment.

I know when my fish got Ick before, I was so worried because I thought I kept seen spots on the other fish.

Just take a deep breath and do research before you act, especially when putting chemicals with your fish, it's the best thing I've learned to do when fish are sick.

I hope you can get them feeling better and back to their normal tank soon!

I had no idea it was so hard to get the fish medication in Canada, I know you guys have Amazon over there.

Ridge Chambers

I set up a new qt last night and put them in there. today I dosed the bifuran. So far they seem fine.

When I put them in the qt I noticed the edges of their anal, pectoral, and ventral find are white.

This seems to be a common issue with corydoras. I hope it's not columnaris.

Ridge Chambers

They have been hiding in the corner behind a rock for the past few hours. One of them hasn't moved, face in the corner. I'm sort of worried.

Edit: they have been swimming around occasionally, mostly surfing the glass.


What substrate do you have? In my prior experience and mishaps I learned the hard way that cories health and wellbeing demands absolutely smooth small gravel or fine sand. Anything else will act as a cheese grater to their mouths and delicate barbells. Over time (most especially if pristine water quality isn't kept) the constant mouth abrasions get infected. If you don't already have cory friendly substrate I would definitely advise either switch to sand and medicate their wounds until you see them heal or rehome them. Some of their barbells will grow back but some may not. Out of 8, 6 of mine grew back fine one had stubs and one never grew any at all. But they were much happier and ate more in sand. There is a fungal infection that can occur among all fish that targets their mouths but if you have rough substrate I would say that's the culprit first.

Ridge Chambers

The substrate in the display is Pool filter sand, which I believe is fine for corydoras. I also learned that lesson the hard way, I was keeping the sterbaI corydoras in my planted 65 with flourite and their barbels still haven't come back fortunately they can still eat.

I had read on multiple forums that flourite was fine but also that it was too abrasive. After some time in the hobby I have come to my own conclusion that every bag of flourite is different, and after a while the sharp edges smooth out like glass on the beach.

Anyways, the affected corys had never been kept on anything other than PFS. On day 3 of bifuran treatment I wasn't seeing any improvement, in fact the fins we're decaying at an alarming rate. I also noticed signs of oxygen deprivation in the smaller fish. I added carbon and performed 25 % WC

Day 4: the decay of the fins seemed to be stopping, but the smaller Cory was no longer eating. He was constantly swimming around mid water, almost weightlessly, though still upright and controlling his movement. I knew he wasn't going to last.

Day 5: came home from work to find the little guy lying on his side, his time had come. The other Cory was still eating and his mouth and fins we're looking better. Later that night, I found him gasping on his side. I couldn't go to bed without doing something to try to help so I cut the bottom of a plastic container. I put netting over the bottom and floated it on the surface so maybe it would be easier for him to breathe. He's gone now too.

I don't usually use meds, but when I do I almost always make things worse. Of course I can't know what killed them, but I wish I had stuck to waterchanges. maybe they would have gotten better if I just gave them some time.


I'm sorry but you did try your best to help them and tried to make the last guy comfortable as he went! Unfortunately corydoras are just one of those species super sensitive to meds and salt which makes it very hard to treat them. I've also noticed out of any fish I've kept my cories transported the worst and withdrew when isolated in QT tanks or treatment tanks. I've lost more to just plain old stress than actual diseases.

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