My spouse has a 450 gallon "pond" with fifteen goldfish two and a half to three inches long. They were sold as "common goldfish" a year or two ago. Cost 20¢ each.

One of the larger ones which had a white abdomen has turned almost completely white within a week or two. It it feeds ravenously and seems to act and react like all the others.

She changed from one brand of food to another about the time of the color change. No color change is seen in any of the other fourteen goldfish.

Any conjectures as to what happened?