You’re staring at your aquarium. It’s late. Everything is quiet. And there’s your fish, floating calmly, fins moving slowly, eyes wide open. Are they... asleep? Or just zoning out? Fish don’t come ...

Culum Brown does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their ...

Fish don’t have eyelids. They don’t curl up in beds or snore, so it’s easy to assume they just keep swimming forever without rest. But they do sleep—it just looks very different from how we do it.

As a lifelong fishkeeper, I’m familiar with noisy fish. Perhaps my favorite noisy aquarium fish are the Synodontis catfishes, which produce a rasping sound resembling a growl that can easily be heard ...