Still too early to tell if fertile or not. It appears to be good. But that's going off a guess at this stage. What your seeing is an air pocket. Chalking will be a band on the outside of the egg where the embryo has strengthened the developing portion of the egg. Keep this photo and take more in another couple weeks. Remember not to leave the candling light on too long and don't do it too often as it can effect temperature rapidly of the inside of egg.