I can't see it from the tank. Will it digest soon?I've seen a barb swallowed before. It's very possible. I really hope that is not the case. The time I've seen it happen, it was fatal.
Have you gone down your checklist of everything else and eliminated other possibilities? Looks like you're barebottom so that eliminates the hidden barb possibility. You're confident he recently shed a stinger barb?
I've heard of anesthesia, ray belly up, and pliers to try and pull it out if you can see it through the mouth in the pharnyx.
This is a tough one