ThRoewer
New member
I have found that one fish alone often acts paranoid, but if you have two fish (or more) the behave much more normally. My interpretation is that having no other fish around is warning sign that something is amiss and that the fish just can't get past that.
Exceptions: puffer fish and other very outgoing exploratory fish don't seem to mind.
I'd recommend getting a pair, or at least two fish.
+1
I observed that several Centropyge (dwarf angels) go crazy if kept without a mate, even if other fish are present. They start swimming rounds along the back or rocks as if they are chasing something. I never observed this when I kept them as a pair or in a harem.