I don't really know anything about fish, but is it possible that it's just pregnant? :)
This might help: http://koifishcare.net/ If you can't find what you want maybe you can write to them.
full of eggs!!!
This is a fancy goldfish, right? If it is, that is kind of the body shape that all of mine are... If it is a koi, I would say pregnant. Is it by itself?
Thinking it is ready to lay eggs and multiply!!
http://www.ehow.com/how_5123460_tell-koi-fish-pregnant-sick.html Here is what I found when I searched your question. Hope it will be of aid to you and your fish...Best Wishes! :)
@LInda I am no expert, but my guess the fish is with eggs. If you look at the pics of bloated koi the belly is swollen to the spine. If you have real concerns, you could take the pic or the fish to your local fish store, they should be able to help.
I have 2 like this that have been this way for several years. I think it's just the way this fish is supposed to be.
I had 3 and they too looked bloated but they were called fantails. However, the third fish got bigger and bigger and bigger and in the end died so not sure what the issue was.