Gills turned black on goldfish

[ElijahTurtle]

Just got an email from my little sister about her boyfriends goldfish.
Apparently the gills turned black on them. Anyone ever heard of this?
I think it's a safe bet that they don't test the water. So getting that info is probably nill

[tsunderl]

Here's what I found on a Google search...

Gills or gill covers? If the gills are indeed black the fish is a goner. But what I assume is the gill covers, the boney plate on the outside of the actual gills, has turned black. This could be a number of things, since the fish is 6 years old, I don't think the fish is changing color. I have never witnessed a goldfish gain black coloration, only lose it. Its a very unstable color for goldfish. Black coloration is usually like a healing scab, but since it is near the gills its a little more serious. Many times when a fish is subjected to ammonia, it will burn the slime coat and fish's skin, resulting when healing a black patch, often seen in the finnage, but not uncommon on the body. Usually it is from poor water quality, or trauma, such as scraping. Scraping may be a sign of any number of pathogens.
Here's exactly what my goldfish book says about blackening (melanophore migration)
"Solutions: In cases of loss of pigment or blackening related to healing, check water quality, activity level, appetite, and whether fins are clear and erect. If these are all acceptable, you have nothing to worry about.
If the discolored areas are depressed or raised, however, you may be facing bacterial infections, parasitism, a skin tumor, a viral wart such as carp pox or lymphocytes, and further diagnosis is recommended." from Goldfish - A Complete Guide to Care and Collecting, by Rick Hess and Dr. Eric Johnson.