Yup that's the marble gene for you! This is the reason for my fascination of marbles and having them as beautiful swimming works f art that obviously love change lol.
He is a very nice looking male. You might also be in store for some extra marbling. He is still young. Is there any particular pattern you would like to see?
Also he might even marble into a butterfly male because the butterfly gene is connected to marbles as well. When breeding a marble and continuing the line, you will eventually end up with some nice butterfly's with some selective breeding in the process.