See if you can quarentine the fish right off.

Usually fish get ill when stressed for other reasons, so check the pond water before anyone else gets it too. Otherwise perhaps it was just the stress of the winter.

The Goldfish and Aquarium Board (GAB) (http://thegab.org/) has good info and a good forum devoted to goldies.

From the GAB: " If the fish has been injured and you see fast growing white/gray fuzz, this is most likely fungus and should be treated with Maroxy (treatment for true fungus). If it is a large fish, you can skip the whole tank treatment and just dab the affected areas with iodine/betadine or malachite green."

Thanks! I think I'll pick up some iodine.

Update!

After almost a month of using the iodine I'm happy to say my sick fish is much better! Although he lost two of his bottom fins, on the same side, he is swimming around with all his fish friends. Yes, he is swimming a little crooked but he isn't laying on the bottom anymore and he's eating and being normal! YEAH! :)