I will re-post this here:

One of my feed corrals is a 10 foot by 2.5 foot rectangle and in the other pond it is a square 3.5 feet on a side. All inside measures, made of 3" DWV PVC pipe and 4 ells.
They seem to be plenty big. The fish (BG and CC) come to the same place every day to get food. When it is not windy (rare) I throw feed along the outsides of the corral also.