Definitely an infection of some sort. It looks fungal to me also. Can you contact a vet? It will progressively get worse if untreated . Vet prescribed properly diluted SSD cream can help but he likely needs a systemic treatment. Call them soon and you can cure him. If you wait too long it's possible you may not be able to reverse the damage, and it may become severe.

Put your baby in a quarantine tank until he is better.