http://swissbaync5d7ykaz7dh7v4qjrb4gmen5aj3bogxrcgbb43ij34bjuyd.onion/pdf/Books/Survival/Medicine/oddsnends.htm
Fish have no eyelids,
so their eyes are always open even though they don't "see" while asleep. Other sea creatures sleep during the day and come out only at night (some species of
octopus, for example, although they are not fishes). Finally, some fishes, notably some
species of shark, appear not to sleep at all.