Mouth Fungus (also known as Chondrococuus; contagious)

A white cottony growth on the mouth, this fungus sometimes spreads toward the gills. This is caused by a bacterium known as Flexibacter. If left untreated for any amount of time it will destroy the entire mouth region of a goldfish and lead to its eventual death.

Again, commercial cures are available. I strongly suggest that you follow their directions to the letter. If you want to, you can begin a salt-water treatment right away if the stores are closed or if commercial chemicals are unavailable. Some people will start a salt bath and then use a general commercial fungal or bacterial control. Consult your pet store owner once you have made your diagnosis.