How Do Fish Breathe in Water?

Fish breathe underwater through a specialized respiratory system involving gills. Gills are feathery organs located on the sides of a fish’s head, protected by a bony cover called the operculum. Each gill is composed of numerous thin filaments that are covered in tiny structures called lamellae, which are rich in blood vessels.

The process of breathing starts when a fish takes in water through its mouth. The water then flows over the gills, passing through the gill filaments. As water moves over the lamellae, oxygen dissolved in the water diffuses into the blood vessels, while carbon dioxide in the fish’s blood diffuses out into the water. This exchange occurs due to the thinness of the lamellae walls and the large surface area they provide, allowing efficient gas exchange.

Also Read: Diffusion

The oxygen-rich blood is then transported throughout the fish’s body, supplying important oxygen to its tissues and organs. Meanwhile, the water, now carrying the waste carbon dioxide, exits the fish through openings at the back of the gill chambers.

This efficient system enables fish to extract oxygen from water, which contains much less oxygen than air, allowing them to thrive in aquatic environments.

Relevant Links:

• Respiration – Definition, Types, Characteristics, Examples
• Inspiration and Expiration
• NCERT Notes Class 11 Biology Chapter 14 – Breathing and Exchange of Gases