I have a fantail goldfish with a red bump right under it's dorsal fin. It is about the size of a pea, and sticks out about 1/16". Has anyone seen something like this or give me any idea what it is? Thanks

It's probably a cyst. There's usually nothing you can do about them. In rare cases, tumors are not harmless but can be cancer or due to various bacteria.

If the bump is in fact not as large as a pea, if could be an irritation spot or injured area. By an irritation spot, I mean a location where an anchor worm (or perhaps a leech or fish louse) was or is attached. Is there a white "string" hanging out from the bump?

A photo would be helpful.

I hope it's nothing!