1. Water enters the mouth: Fish open their mouths and take in water.
2. Water flows over the gills: The water passes over the gills, which are located in the pharynx (throat) area.
3. Oxygen diffuses into the blood: The gills are composed of thin, folded tissues called gill filaments. These filaments are covered in tiny blood vessels called capillaries. As water flows over the gills, the oxygen dissolved in the water diffuses from the water into the capillaries.
4. Carbon dioxide diffuses out: At the same time, carbon dioxide from the fish's blood diffuses into the water and is expelled.
5. Water exits the body: The water, now depleted of oxygen and enriched with carbon dioxide, exits the fish's body through the gill slits.
Key points about fish respiration:
* Fish gills are highly efficient: The large surface area of the gill filaments and the thinness of the capillaries allow for rapid gas exchange.
* Fish need to keep moving: Most fish need to constantly move water over their gills to get enough oxygen. This is why they are constantly swimming or using their fins to create currents.
* Some fish are adapted to low oxygen environments: Some fish, like catfish and carp, have adaptations that allow them to survive in waters with low oxygen levels.
* Oxygen content in water varies: The amount of oxygen in water can vary depending on factors like temperature, pressure, and the presence of algae and other aquatic plants.
Let me know if you want to know more about specific types of fish gills or how fish breathe in different environments!