For most fish, the line Dory utters in the popular Disney movie “Finding Nemo” is no exaggeration. Sounds exhausting, right? But you’re unlikely to catch a fish closing its eyes for a quick catnap.That’s partly due to the fact that most fish don’t have eyelids. But it’s also because fish don’t technically sleep—at least not like we humans do.In a watery world of predator vs. prey, deep sleep isn’t really an option. Instead, most fish find ways to reduce their activity and metabolism while still remaining alert.Us humans spend our time a little differently. In fact, nearly one third of our lives are spent asleep, but we’re hardly the heavy-hitters of the animal kingdom. Plenty of other species enjoy a good snooze.