I have fish that sleep so sound nothing would wake them--and I have fish that appear to never sleep at all. I had a hippo tang that would totally lay on its side, flat as a pancake for hours. (imagine my dismay every morning for a while when he was new--I was sure he was either dead or dying but nope had that fish for almost 5 years.) My picasso wedges himself so tight in a piece of lr sometimes he actually comes out with scrapes. He is a lazy fish, at least till supper time. My queen angel never sleeps, once in a while she'll sit behind a rock but never for more than fifteen minutes, even at night I know this because we have a baby who is up half the night and she always seems happy to see us.