The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
First off, it appears the fish is actually disfigured so there may not be anything wrong but as the fish is growing, the area with the missing line just gets more exposed because the scales in that area never had the blue line. That said, the back area of the fish is distorted in the picture so you want to make sure there is no raising of the scales or areas of missing scales. If there isn't any of this, I wouldn't be concerned.