Clean water is vital for breathing

ALL animals need oxygen to help them get energy from their food. Most fish and many other water-living animals get their oxygen from the water, instead of from the air. They have special parts called gills which they use to breathe.

Gills are thin and feathery. Many animals, such as fish, have them inside their bodies, under a flap or gill cover, but others, especially young forms such as tadpoles, have them sticking out from the sides of their heads. These are called external gills.

The fish 'breathes' in water through its mouth. Oxygen from the water passes into the blood in the gills, and is carried around the body.

Carbon dioxide produced in the body is carried back to the gills in the blood and passes into the water from behind its gill cover.

Many insects and animals have other ways of getting oxygen. Whirligig beetles carry an air bubble under their wings which they use to breathe under the water for a few minutes.

Water spiders carry bubbles of air under the water and keep them in a net attached to stems. They eat insects and fish in their bubble. Though tadpoles have gills, adult frogs have lungs and breathe air, but they can also take oxygen through their skins from air and water.