As mentioned, they are stress marks. However, please keep in mind that stress marks are not always a sign of stress. It can be a sign of feeling dominant/aggressive, or being a bit cold. Your guy has very light stress marks in that picture - nothing to worry about. He may feel a bit cold out of his tank, or may just a bit uncomfortable the way he is perched on your hand. It can be hard to tell, but they come and go and aren't normally a sign of any issues unless they are very dark and persist for a long time.