It sounds like you have Mouth Fungus or Columnaris, caused by Flexibacter
In my experience overcrowding, insufficient water changes and keeping
temperature too high can contribute, so even when you successfully treat
with antibiotics it will tend to recur unless you correct the underlying
If you have access to them the antibiotics of choice seem to be
Tetracycline or Chloramphenicol.
Bruce Hansen, ANGFA, caring for our aquatic ecosystems.
Please visit us at http://www.ozemail.com.au/~fisher/angfa.htm
> From: Marcel Beekman <marci at wxs.nl>
> To: rainbowfish at pcug.org.au
> Subject: [RML] Mycosis?
> Date: Wednesday, 14 January 1998 0:25
> With Marcel Beekman also a Newbe under the rainbowfish
> enthusiasts. I've a problem: My rainbows sometimes have
> a kind of mycosis at the mouth.
> I don't know what the problem is. May be the aquarium is to
> crowded, i have 13 Melanotaenia splendida rubrostriata's, 1 M.
> maccullochi, 5 Corydoras schwartzi and 2 Peckoltia vittata.
> Sizes of the rainbows varying from 6 to 10 cm, in a aquarium of
> 100x50x50 cm.
> Nitrate values seem to be OK, pH is 7.2, KH is around 3-4 °DH,
> and GH is around 6-7 °DH. Plants are growing fast.