biggest goldfish has "buffalo hump" why?

[susanp]

I have 2 10-yr-old feeder goldfish, both about the size of a large hand.  One is normal goldfish shape, head and back more or less aligned.  The slightly larger, more robust fish has a huge hump-shaped back that is significantly higher than his face.  Why is this, anyone?  It makes him look kind of tough!

[helenf]

Can you post a photo of the goldfish? 

Goldfish have been bred into all sorts of weird shapes.  Pet shop goldfish often have a very mixed ancestry, meaning that they can come out looking quite different from one another, depending on their genetic makeup.  So it could be just his genes.  Or, on the other hand, it could be the site of an injury or infection or some problem.

If he seems otherwise happy and healthy, I wouldn't worry about it.