Barb with tail damage

I have a Rosy Barb with a chunk out it's tail just ahead of the fins. The
wound looks fairly round like an Ulcer or something that popped. But it
could also be an attack from another fish(es). The fish is still active and
eating, but I'm still tempted to pull him out. I've lost a few Barbs (4)
over the past few months, one at a time. All looked like they'd been pecked
at. Before or after death I can't say. I'm also missing a Tetra, but they
have been in there for months. I'm wondering if one of my SAEs is a CAE in
Sheep's clothing.