These are great little fish to keep in a friendly community tank, they are very delicate and almost remind you of a hummingbird the way they roam the tank grazing on tiny bits of algae and other bits. I have had may varieties of Pencilfish over the years and they all seem to be timid so keep them away from any aggressive fish.
These fish do best in groups of at least five. Males have brighter red fins than females, and will often 'fight'. It isn't real fighting, though, they just circle and then sort of body-slam each other a few times before somehow declaring a winner. They don't hurt each other at all when they're doing it, and it doesn't seem to stress them, it's more sparring than anything else.
These are one of my favorite fish. I have nine of them in a large tank. The way the males battle is very different then most other tetras. They face down and wiggle back forth there color is really bright when there fighting. No one gets hurt but it goes on all the time. Fun to watch!!