Respiratory system of a fish Simplified diagram of a fish's respiratory system, showing the location of the gills and the direction of water flow used for gas exchange. (more) How Do Gills Work? Ask the Chatbot a Question More Actions Share Share Share to social media Facebook X URL https://www.britannica.com/science/How-Do-Gills-Work 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 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.... The Editors of Encyclopaedia Britannica Last Updated: Sep 8, 2025 • Article History Table of Contents Table of Contents Ask the Chatbot Gills help aquatic animals breathe by allowing gases to move between water and blood. Their feathery, branched structure is filled with superficial blood vessels, which gives them a large surface area for this exchange. This design brings the circulatory system very close to the water, making it easier for oxygen to enter the blood and carbon dioxide to leave. In fish, water enters through the mouth and flows over gill filaments supported by gill arches. Oxygen passes into the blood while carbon dioxide is released into the water. The blood in the gill capillaries flows in the opposite direction of ...(100 of 227 words)

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