Posted by sally kentch on May 30, 2007

Q: Do fish sleep?

State: Washington

A: An excellent question! Actually, scientists are still not entirely sure why humans sleep or what sleep is! Oh, there are the obvious benefits (rejuvenate our bodies, for example) but there has been a lot of study on sleep in humans and still much, much more to learn. So, this makes it a bit difficult to determine whether fish sleep and what they might gain from it too.

However, it does look as though fish sleep or approach something that is very close to what we think of as sleep. If you've ever had a goldfish in your home and came into the room late at night and turned on the light, you may have noticed that your fish was simply stationary (often lying on the bottom) in the tank. Even though fish can't close their eyes without eyelids, despite their open eyes, they're probably in some sort of "sleep state". Divers who have swum around reefs at night regularly find fish that are wrapped in a kind of mucus-like cocoon of their own making, are immobile and seem to be asleep too. Kind of interesting, isn't it?

So, if you're asking me if fish sleep, I'd have to say they probably do but I can't say for sure. This might make a good research project for someone in college someday - hint! Thanks for asking.

John Wiessinger ( May 30, 2007)