Fat goldfish

Question
I have a 6-7" gold/white goldfish that is swollen right below the tailfin area.  It has been that way for about 6 weeks or more.  Is it going to have babies or is it sick?  It will stay at the bottom alot but will move around when feeding.

Answer
When egg-laden, a goldfish will be fatter in the abdomen but not grossly so.  Is this a single lump or is the whole area swollen?  What variety of goldfish is it (fantail, comet, etc.)?  Fancy goldfish are more apt to appear fat.  I suspect that the swelling is not normal or an indication of being egg-laden.  I have a section entitled "Why is my fish fat?" at http://www.fishpondinfo.com/health4.htm#fat
I hope she's not sick!

Robyn