Hi folks,

These are photos of one of my girlfriends two goldfish:

http://www.b0rken.org/~jason/fish1.jpg
http://www.b0rken.org/~jason/fish2.jpg
http://www.b0rken.org/~jason/fish3.jpg

As you can see, he has black markings just above his mouth and around his
gills.

The little "moustache" marking has been there about a week. I initially
thought it was bruising from where he likes to swim into the side of the
tank, but over the last 2-3 days, the gill markings have appeared too. The
black marks around his eyes have always been there.

He doesn't seem distressed in anyway, and still eats like the a glutton.

The other fish is unaffected.

They have recently been moved into a new tank, which is much larger and
cleaner than their old one. That was 3 weeks ago.

Can anyone tell me what those markings might be, and if it is an ailment of
some kind, how to treat it?

Many thanks,

Jason