Being a fancy goldfish sissy you have to think about what this has done to the fishes insides their internal organs are all sort of scrunched up inside the body cavity.....
As such this leaves them open to a ost of problems the main one being a swimbladder disorder normally caused by it eating where it presses on the swimbladder giving them problems with bouyancy .
Try a diet of peas and cut up earthworm in future as this acts as a sort of natural laxative clearing its stomach out and stopping the pressure on the swimbladder thus correcting its upside down posture
The number of people that have asked me to help with the facy varieties makes me all the more detemind that something should be done about this , possily this trait be bred out of the fancy varieties that are the most proneto this.
You see the same thing happening in the some of the pedigree dogs I've seen especially with the lap dogs and bulldog breeds where they have problems with their soft palet and thus their breating , Poodles can in later life go blind in the two smaller types and some spanielsare prone to fits because the brain is to large for the skull Pekcenease lap lap dogs can sneeze ejectiog both eyes from the head one breed of bull dog has to have a C section to give birth as its pups are too large to be born naturally I could go on and on , moves in the UK are now afoot to change things so you can see its mans fault both are shaped like they are and their are miriads of other fancy breeds that have problems ( thats why we love koi) the body shape remains the same, its just the colour gets changed .
rgrds
Dave
PS I agree that the dog possibly picked it up bcause of this.