The following URLs link to pages about fish diseases. The actual link
may go to a specific disease that has nothing to do with what your fish
has, but you should be able to navigate from there to an index or
similar type page. Hopefully you will find pics and descriptions to
help you ID the disease:

http://www.fishdeals.com/fish_diseas...sdisease.shtml

http://www.fishkeepinguk.co.uk/disease.htm

http://faq.thekrib.com/disease-fw.html

http://www.pkpets.com/pets/fishdisease.htm

http://www.suite101.com/article.cfm/aquariums/1770

http://www.aquarticles.com/articles/...er_FishTB.html

http://www.fishpalace.org/Disease.html

http://www.exitfive.com/fishdoctor/skinbody.html

....I got these from a thread on a forum elsewhere, so I don't know how
good any of them is, but I'm sure you'll find somthing useful.

I would not just ignore it and hope it goes away - quarantine the fish,
research and treat him (and others / the tank, as needed, to avoid it
spreading and killing more fish).

Liz