Something’s fishy: While you were sleeping

Atlantic whitefish (Photo by Bob Semple)

Atlantic whitefish (Photo by Bob Semple)

October 28, 2019 | by Raechel Bonomo

There are few things I love more than a good power nap. As an avid runner, I put my body through a lot, and rest is an important part of the training process. But sleep is essential for all humans, regardless of how many kilometres we are clocking. Without sleep, we wouldn’t survive.

But what about fish? Do they sleep and, if so, how?

While I write about many different species and conservation-related topics in my role at the Nature Conservancy of Canada, it’s safe to say my biggest splash here is the Something’s Fishy series. After many blog posts on the fish that occupy waters in and around Canada, I’ve never thought about how they recuperate after a long migratory swim or a day jumping out of the water for food.

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The easy answer is yes, fish do sleep. Well, kind of. One thing’s for sure: they don’t sleep like we do.

Many fish species lack eyelids and cannot close their eyes, so any sleeping is done is with eyes wide open. Creepy! Most fish species lack a neocortex — the part of the brain in mammals that is responsible for the neuro-activity that happens during sleep.

Smallmouth bass (Photo by U.S. Fish and Wildlife Service)

Smallmouth bass (Photo by U.S. Fish and Wildlife Service)

While scientists are currently studying this area of fish life, it’s safe to say that fish don’t require the recommended six to eight hours of shut-eye that humans do. It’s more accurate to say that fish don’t sleep, they rest.

The lack of sleep in most fish species can be tied to the limited sensory input in their brains, which doesn’t need time to recharge or reset like in mammals. It’s believed that some species of fish may reduce their activity for a short period, which slows their metabolism. Fish like sharks and tuna never stop swimming. With no pillow or blanket in sight, the fish appear to be floating in one spot or wedged within a secure spot. They may seek shelter between rocks or in mud, but they sometimes seek out other fishes’ nests for a quick nap.

It’s not currently known what the benefits of sleep or rest are to fish, but it may provide benefits similar to those in mammals. I know I can’t do without my seven hours of sleep each night; without it, I feel like a zombie in a spell that not even coffee can snap me out of.

Raechel Bonomo (Photo by Chase Wastesicoot)

About the Author

Raechel Bonomo is the internal communications lead at the Nature Conservancy of Canada.

Read more about Raechel Bonomo.

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