How do fish breathe underwater

Описание: Fish breathe underwater using specialized organs called **gills**. Unlike humans, who use lungs to take oxygen from air, fish extract dissolved oxygen from water. As a fish swims or opens and closes its mouth, water flows in through the mouth and passes over thin, feathery filaments inside the gills. These filaments contain tiny blood vessels called capillaries.

Oxygen in the water moves into the fish’s bloodstream through a process called **diffusion**, where oxygen travels from an area of higher concentration (the water) to lower concentration (the blood). At the same time, **carbon dioxide**, a waste gas in the blood, diffuses out into the water and is expelled as the water flows out through the gill openings.

Many fish also use a system called **countercurrent exchange**, where blood flows in the opposite direction of the water movement. This maximizes how much oxygen the blood can absorb, making the process extremely efficient.

This amazing system allows fish to survive and thrive in environments where breathing air would be impossible. However, fish still need well-oxygenated water; polluted or stagnant water can contain too little oxygen, making it difficult or even impossible for them to survive.