Other than the information already posted about which species have which activity level, I've noticed that it really strongly depends on what the tank-mates are. I've got a tank that's basically Bichir dominant, and there are only a few Distichodus and a school of 6 Coppernosed Barbs, but the main # of fish in the tank are all Polypterus. In my tank, and in JESToner's tank (99% Bichir only) the fish seem to be a lot more active and relaxed, not to mention very social and communal with eachother. In tanks that are just mixed fish, with a few Bichirs mixed in, I've noticed they dont seem as comfortable or active.