Imagine my surprise and utter dismay when my favorite rainbow shark (Leroy) looked as though he'd messed with a slutty mermaid!
As it turns out, Leroy was suffering from a known condition known as mouth fungus (although it is actually a bacterial disease). It's most often found in tanks that have high bacterial loads and need require frrequent water changes and gravel vacs, overfeeding can lead to this nasty looking fungal infection as well. The disease is Flexibacter columnaris (so by now you realize I am a show off nerd).
Treatment: Isolation, treatment with an antibiotic (same as if he had actually hooked up with that slutty mermaid) and lower water temp (between 74-76 degrees (the bacteria actually thrives on higher in higher temp.