I did some research for you and found two likely possibilities one is parasites but I'd expect all the fish to have an issue then. The other is called Dropsy where symptoms would be a swollen abdomen and scales sticking out. You can read about the condition and treatment here
http://www.goldfishinfo.com/ailment1.htm#dropsy
The pond fish can have the same problems as the tank goldfish.
It may have started as constipation but now may have gone beyond that to dropsy. You can read about constipation here
http://www.kokosgoldfish.com/Constipation.html
Hope this helps you!
Edited by NHolmes on September 21 2005 at 1:04 PM
Please press Accept if you find my answer helpful. Want more info? Just reply on your question!
Bonuses for good work are always appreciated!
Thanks for the opportunity to help you!