When you check a hole or a small cave looking for any fish living there, they get flat next to the ceiling trying not to be seen. To observe them well you have to look from a lower angle and then waiting motionless till they feel more confident. Inexperienced divers who dive too far from the sea bed often see only the really big fish and/or the ones living outside caves. Photographers know this well and learnt how to wait and even not breath trying to avoid bubbles that might scare the fish.

This behaviour is even more common if in that area underwater fishing is allowed. Only in more rarely visited marine sanctuaries where scuba diving is not so popular fish behaves even curiously approaching you.