Extreamly Fat, floating goldfish

Question
About 4 years ago i bought 2 goldfish and they lived in a tank for about 3 years, but last summer i put them both in my new pond. During there time in the tank i noticed that one of them started getting a little fat, but thought nothing of it. Since its been in my new pond, its became alot fatter and it started to some times float upsidedown. But now it is nearly constantly floating upside down and is struggling to feed as it cannot stay upright.

Answer
Hey Sean,

Sounds to me like the late stages of a swimbladder infection. Typically, this is regarded as incurable, but as long as the fish continues to eat, it's workable. Isolate the fish, and track down swim bladder infection medication at your local pet store. Also, switch foods to thawed peas cut small enough for it to eat. These two changes should help ease the fish, and perhaps start to heal it as well.

Best wishes, and good luck