How is his calcium intake? Is he still soft like a hatchling? If he hasn't firmed up yet he should soon with calcium and sun light.
It looks reminiscence of really bad cases of MBD where the shell is so soft and thin you can see through it. I'm not saying that is what it is. I am saying if your husbandry is in check than it looks like nothing to worry about.
He has a cuttle bone that he nibbles on at free will. I don't give him any other calcium. There is still a little bit of give but it's definitely not mushy and not see through at all.
What does your tortoise weigh and how old is it?
What is your UV source?
If your tort has had issues with possible metabolic bone disease, and I don't know if it was ever a problem, I would definitely give him calcium supplements. A cuddle bone may not be enough especially if he doesn't chew on it. In any case, I strongly recommend the calcium D3 because of the softness. If he's just a couple of months, it's normal that there be some give. But, your original concern is still about growth lines, in my opinion.
That's what I thought. But, if you want to ward off any future problems, you'll need to get a UV bulb for the times he can't get the natural sun especially in the winter months when the temps outside are too cold. If he's eating the cuddle bone, then I agree with you, he may not need the calcium supplement. Keep an eye out for how often he chews on the cuddle bone cause if he's eating it every once in a while, he should be getting calcium about 3 times a week. Other than that, Tom can chime in and give you his expert opinion. Again, those are growth lines, and nothing to worry about.I just read about metabolic bone disease here:
http://africantortoise.com/metabolic_bone_disease.htm
And tortie has none of the "critical signs" of MBD.
That's what I thought. But, if you want to ward off any future problems, you'll need to get a UV bulb for the times he can't get the natural sun especially in the winter months when the temps outside are too cold. If he's eating the cuddle bone, then I agree with you, he may not need the calcium supplement. Keep an eye out for how often he chews on the cuddle bone cause if he's eating it every once in a while, he should be getting calcium about 3 times a week. Other than that, Tom can chime in and give you his expert opinion. Again, those are growth lines, and nothing to worry about.
What does your tortoise weigh and how old is it?
What is your UV source?
The bruising is not normal, and it can be an indicator of a very serious problem, but your tortoise doesn't show any of the other signs.
I think the thing to do is just keep an eye on your tortoise and make sure its getting as much mid day winter sun as it can.
What are you feeding him?
@Tom Are you saying that the discoloration are bruises, or that " bruises" in general are not normal? I'd be very surprised if you believe the discoloration are bruises cause my torts had those same discoloration and they were growth lines that later got lighter, and they didn't have (nor ever) had MBD.
That sort of discoloration is not normal. Pinkness between the scutes in the areas of new growth is normal, but I've never seen that sort of dark smear.
I don't know what it is.
I stand by my prior recommendation of keep an eye on it and make sure the tortoises gets lots of sunshine.