HammIamm,
Sgtbirch is correct. Your fish has mouth fungus, otherwise known as Columnaris. It is contagious and fatal, unless caught early enough to administer the appropriate medications. Even tho it is known as "mouth fungus", it is only known as that because of its appearance ... when in fact it is instead a bacterial infection, caused by Flexibacter columnaris, and can only be treated with the appropriate antibiotics. Antifungals and fungicides will be rendered useless against this infection and may even further suppress the fish's disease resistance.
In order to save your fish, you must act quickly, because fish can succumb to this infection within just a few days' time.
Please note that Columnaris/mouth fungus is most often caused by poor water quality and inadequate nutrition, two factors that you may want to examine in order to avoid future infections !