Anyone know what these marks on my porcupine puffer are?

[alang_94526]

I bought a porcupine puffer about 4 weeks ago and it has been very lively and eating well.
Today, I noticed large white marks on its back.
I don't know what it is and wondered if anyone out there does.

 

[johnnyriker]

If it's only on top I would guess he is burning from too much light.