This is a video on youtube of someones black moore. He has a sizeable lump near his tail which is very obvious when you see it. Does anyone have any answers as to what this may be??
Thanx.
http://www.youtube.com/watch?v=k0NmXgGZFSM

This is the video link. If you can't just click on it, cut and paste into your browser. Cheers.

Certainly looks like a very large cyst. This could be nodular disease which can be caused by parasites. There is a possibility that this is very infectious so isolating a fish is a good idea. According to my fish health book, there is normally no reliable treatment for these type of diseases. If the condition gets very bad, euthanasia is normally the only option.

That looks really nasty. If euthanasia is being considered I would think about giving cutting it out a go. My thinking is that the fish would at least have a chance, only problem is the question of pain and hurt to the fish!

First, I have no earthly idea what that is. It has been my experience though with Fancy Goldfish that if they've got a sack or a portion of they're body that is full of fluid, cutting or piercing it will kill them. Some chubby bodied type goldfish can drain to skin and bones. I've got a Black Moor in front of me right now though and I'd have to say that whatever that is, it's more likely a cystic sort of mass. There is a lot of meat up there on the fish back. If I had one that looked like that I'd quarantine it, but I doubt I'd treat it. Just sort of a wait and see operation. Fancy goldfish are so inbred that who knows what kind of weird mutations you're going to see.