Birth defect?

[1beataway]

I've had my second blue dumpy since like January, and he's always been in the same tank as my other. When I bought him, he had a barely noticable bump on his back. I notice that it looks much larger now. It feels like it's part of his skeleton. Think it's just a birth defect and won't cause any problems? He moves around very well. He eats (he's not as chubby as my other dumpy, but he's the first after the crickets, and he'll eat a mealworm or two when I feed them). Mostly, that bump just looks bigger.