I Didn’t Know That

Q: Do fish sleep?

A: Some apparently do, according to Ken Yates, vice president for husbandry of the Aquarium of the Pacific in Long Beach. Tropical fish, especially, appear to become quiescent at night and their color pattern changes, becoming darker and duller. If you suddenly shine a light in their eyes, he said, they undergo photo-shock: Their fins become erect and their movements become jerky and almost panicky, like a human being startled from sleep. Other fish, he said, are quiescent during the day, hiding in holes and caves and coming out at night. Many of these fish are deep red, he said, which makes them difficult to see at night.