I don't know why he/she does it. But I have had this fish for around 6 months and every once in a while it will "bounce" up and down in the water several times. No one is bothering it that I can see. Is it just letting others know that's it's turf or what? Its the only one that I have seen do such a thing. I can tell its him because a while back it got poked by my urchin, maybe 4 months ago. So one eye is jacked up a little.