Deformities like this come naturally from birth. You don't see these in stores because people do what is known as culling.
They kill the fry (hopefully humanely) that have negative traits - bad coloring, deformation small bodies so the ones with good traits - large, flowy fins, hardier immune systems survive and pass on the genes.
Your fish will most likely live fine but if it breeds expect more fish to look like that you don't want it in the gene pool but don't just go killing it now if you can avoid breeding in any way I'd suggest that.