Need help on my new buy Oranda pectoral fins

I bought 3 orandas (2~3") on sunday from a LFS and kept in my 2 ft tank.
Yesterday, I found one of the fish pectoral fin seem to have some defect. I seldom seem both side of the pectoral fin moved, most of the time one side or none during swimming. I can't describe in detail what is the problem on the fin. The fish sometimes seem floating upside down or side way.

Feel so sad that a new bought fish become this state.
I think the fish has this prob alreadi before I bought it.

May I know is there any cure on this defect or illness?


Thanks a million.