I've done a quick search to prove or disprove my comment that they are schooling fish. The results were inconclusive. This comment from their profile on Badman's Tropical Fish seems true to me: "Preferring to be kept in schools when young, they tend to form smaller groups when mature. When kept in small groups this nocturnal fish will be seen out and around more often during the daylight hours. ", but there was no real consensus of opinion on the Net.
From my own experience I know the ones I have kept have been much more active during the day when kept in groups of three. The first one I purchased was always hiding,the guy in the LFS suggested I put two more in and the diffrence was unbelievable. Very active, swimming together and chasing each other all over the tank.
Easily my favorite fish. Just be careful when netting them. Also be careful when feeding them live fish. They seem to be fairly subsceptible to ich and you want to be careful when introducing untreated feeders that you don't introduce ich into the water.