Why do fish breathe underwater?

When your child asks, here's how to answer — in their words, and in yours.

For your child

Fish have special parts called gills, which are like tiny filters that can take the air out of the water! Just like we breathe air from around us, fish take the air they need right from the water they swim in.

Heads up

The answer simplifies the complex diffusion process and the detailed structure of gills (gill arches, filaments, lamellae). These specifics can be revisited when the child learns about gas exchange or basic biology later on.

For you

Fish breathe underwater using gills, specialized organs that extract dissolved oxygen from water. Water enters the fish's mouth, passes over the gills, and then exits. As water flows over the gill filaments, oxygen diffuses from the water into the fish's bloodstream, and carbon dioxide diffuses from the bloodstream into the water.

They might ask next

What do gills look like?
Do other animals breathe underwater?
Why can't people breathe underwater?

Whyzard answers your child's own questions — out loud, in words they'll understand.