A while ago, I posted a photo of an ember parrotfish missing a chunk from its back (here), but able to carry on quite normally.

In this photo, a bluespotted cornetfish has had its back end removed, likely by a larger predator. However, it too seemed to be getting around fine, though the tail fin is certainly one that cornetfish use a lot.

The other thing about this photo is that it nicely illustrates why this species is called the bluespotted cornetfish.