Thanks you so much. I was very worried there.No, that's not shell rot. To be honest, I don't know what it is. It appears to be inside the shell, under the top layer of keratin. Might just be normal coloration for this particular tortoise, might be a bruise. But I don't think it's anything to be concerned about. Just an FYI - shell rot first shows up on the bottom shell (plastron), not on the top shell (carapace).