I'd pay particular attention to the possibility of TB, which excuz mentioned. It may be a parasite, but if it is possible that it is TB you want to exercise extreme care to not expose yourself.
Thanks for the repsonses so far. I must say that I'm not thrilled with the possibility of Fish TB.
jpappy, I haven't had a chance to get water parameters for you. This tank holds bristlenose plecos, diamond tetras and a pair of silver dollars.
excuzzzeme, there is nothing in the tank that can cause a puncture wound. This was a definite deterioration of the flesh in that area.
dixienut, I don't know that anything actually came out of the hole.
I came home from work one day and my 10 year old son said the fish had a hole in it and puss was coming out. I never saw any "puss". I figured he saw the flesh wasting away from that area.
pinkertd, I haven't bought a new fish in about 3 years. The silver dollars are older than that. My plecos and tetras spawn alot, so I don't need new fish. I have plenty. No, not overstocked though. I have numerous tanks.
All of the inhabitants look healthy. Heck, the silver dollar in question doesn't even act sick.