Can't really tell from the photos, but cabbage maggots do this type of damage. http://www.extension.umn.edu/garden/insects/find/root-maggots-in-home-gardens/ http://vegnet.osu.edu/sites/vegnet/files/imce/April%2016%2012.pdf http://www.fullcircle.com/goodfoodlife/2015/05/28/how-to-keep-your-vegetable-garden-free-of-root-maggots/

Thanks for your reply, farmerdill. Here are a couple of closer shots of the damage. It looks like tiny holes barely drilled through the red skin to the white flesh. There is no discoloration at all. Just those tiny holes. No worms or creatures inside the radish. I had just washed them so they're wet which makes the holes look a bit pink instead of white.

I almost wondered if it was a 'burn' from the soil/fertilizer.