they also dream, something we may never find out. Some parrotfish species in the tropics excrete a cocoon of slime which may deter predators, or just cleanse their skins. Many species are so drowsy when sleeping, that they can gently be held and returned to their bed. (We prefer to catch fish for our aquariums at night, and do so with a tiny hand-held scoop net that we gently place over the sleeping fish. This happens in the bright light of a diver's torch. It does matter what time one dives, as fish become more dopey later at night.) Fishes of the open ocean sleep in schools, but predators able to hunt by night, such as dolphins using sonar, can still locate and attack them. When sleeping, fishes do not like to be thrown around by waves, so they find a tranquil spot inside a cave, behind a sheltering wall, and so on. Pelagic fish that sleep in the open ocean, descend to where waves are no longer annoying. Reef fishes that depend for their entire lives on the rocky substrate, would die if they were swept away by currents. So they sleep close to the rock in sheltered places like cracks, where waves and currents cannot reach. Some semi-pelagic nocturnal fish are able to find their way home again, even when the reef where they sleep is far out of sight. the night shift Many fish species are active by night. They are able to hunt with their eyes