In an article I read, concerning a zebra danios, this could be the result of inbreeding.

That is a result not of inbreeding but of vitamin C deficiency and/or electricity in the water... the spine deforms.... it's permanent... all sources recommend euthanizing the fish for its own good.

Source for diseases of Goldfish

Thanks for the response, he has since passed away and been replaced by calico fantail. How in the world could electricity get in a tank?
Shelley

Stray voltage from things like heaters and filters. Not necessarily your tank, but the breeder's tank or the store's tank before you.

Sounds more like bad genetics to me, especially if only one fish is affected. I have a Pracox Rainbow fish with a vertical rise in his spine. He's healthy in every way, just doesn't look perfect.

Swaybacked? Sounds like King Triton was too big and riding him too hard.
Sorry I had to get that in there.