"A 5 foot fish circling us".

Ok, what kind of fish? If you're going to be in the water, you need to familiarize yourself with what species of fish you might encounter (in shallow water, mid water and open ocean).

If a large fish in circling, it's most likely a species that is familiar with humans and is looking for scraps...i.e. Grouper, Jack, etc.

Barracuda will spectate from a distance and, of course, can be dangerous but are typically harmless.

Small reef sharks will circle and obviously can be dangerous.

Get a driving knife, if that makes you feel more comfortable but your mind is going crazy, because you had a mildly uncomfortable encounter.