Unlike humans and several other mammals who settle in for a cozy night of rest, most of them remain in motion and don’t close their eyes.
Actually, they can’t close their eyes because they lack eyelids.
Some species continue to float along and will occasionally move a fin to keep oxygen flowing into their gills. These subtle movements are also meant to help them stay balanced.
However, in general, their movements are often slower, and many times they’ll drift down toward the bottom of the surface rather than swimming at their normal elevation.
While most of them stay awake during the day and rest at night, there are some kinds that are nocturnal. And still, others do decide to find a safe place and hide from predators for the evening. One notable difference between humans and water-dwelling creatures is that they tend to stay somewhat alert while they’re asleep so that they can escape predators should the need arise.
Unlike humans, they do not seem to follow a circadian rhythm as strictly as we do. They’ll easily adjust their sleeping patterns to water temperature, food availability, migration patterns, and even whether they’re new parents taking care of babies. So, we can potentially take that last part back because new human parents tend to miss out on rest, too!
