goldfish that has lost h bottom fin

Question
have a goldfish that is approximately 2 years old that spends summers in an outdoor pond and winters in a 55 gallon in my basement. Late summer I noticed it swimming rather erratically and thought it was dying. I treated the pond with a natural remedy that I use that I purchase at a local store. She seemed to be better but continued to swim upside down frequently. Recently I moved the fish to the basement tank and noticed that this fish has lost 1 of it's bottom fins.She now swims upside ALL the time at the top of the tank. She eats and will swim normal to get food. I guess U have of you is.....Will this fin grow back....as I assume this is what is causing her to swim upside down....
Any thoughts or ideas....This has been going on for at least 6 weeks...... Hope you can help !!!!! Thanks so much!!!

Answer
Hi Sue:  The fin will eventually regenerate.  Typically  fish that swim on their sides or upside down have either swim bladder issues or an intestinal blockage.  If you are feeding pellets I would suspect the blockage.  In either case I would switch her diet to a brine shrimp only diet for the next week.  This will help clean her out as the shrimp have tiny shells that act as roughage and it will provide her with a great source of protein to help her fin regenerate.... Let me know... dave