Shoal of colorful fish in Belize Fish experience a restful state distinct from mammalian sleep, marked by minimal movement and continued environmental awareness. (more) How Do Fish Sleep? Ask the Chatbot a Question More Actions Share Share Share to social media Facebook X URL https://www.britannica.com/science/How-Do-Fish-Sleep Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback Our editors will review what you’ve submitted and determine whether to revise the article.

　　External Websites Ask the Chatbot a Question Written and fact-checked by The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors. The Editors of Encyclopaedia Britannica Last Updated: Apr 7, 2025 • Article History Table of Contents Table of Contents Ask the Chatbot Fish enter a restful state marked by minimal movement and decreased responsiveness. During this time, they maintain their balance and continue slow, gentle movements, allowing them to conserve energy while remaining able to respond quickly to threats. Although this state resembles sleep, it differs in several ways from the deep, sustained sleep experienced by mammals. One key difference lies in the physical signs of rest. Unlike mammals, fish do not have eyelids and therefore cannot close their eyes while resting. Instead, they remain partially alert, able to sense changes in their environment even as their activity slows. Different species of ...(100 of 251 words)

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