Re the fat discussion: Goldfish are bred to be "fat" in one sense (in the shape of their body, in how they are built), but that is not the same thing as them being "fat" in the obese, unhealthy sense. Look at Greyhounds compared to bulldogs. They are just built differently. If a greyhound was as big around as a typical (not obese) bulldog, it would indeed be fat (in the obese sense). And bulldogs can be obese, but if one were as thin as a greyhound there would be something wrong, because they were not bred to look like that.
So yes, fancy goldfish are bred to be "fat" in a sense, but that does not mean they are naturally obese or unhealthy. If they are well maintained there is nothing wrong with that kind of healthy "fatness" anymore than it is wrong for a bulldog to be "fatter" than a greyhound.