Bob-
Probably just a birth defect...kinda like fish scoliosis. I have seen this a few times over the years. One was a winter brat and I showed it to a biologist friend and that's what he thought it was. There was absolutely no marks or scars suggesting that in was due to an injury. He stated that if it was due to an injury when the fish was young it would have some sort of healed scar and mine did not. It doesn't look like this fish did either...did it?

Talk to you soon!
CM