Sunny the Goldfish's Secret

Quick answer

Fish breathe by moving water over their gills, which grab oxygen from the water.

Lesson

Before school, Leo pressed his nose against the fish tank to say good morning to Sunny the goldfish. Sunny's little mouth went open, shut, open, shut, all the way underwater. Leo held his own breath and puffed out his cheeks — he could only last a few seconds in the bath! So how could Sunny stay under all day and all night?

Leo looked closer and saw something surprising: water was flowing right INTO Sunny's open mouth, again and again. Sunny wasn't drinking it — she was breathing it! Because water has tiny invisible bits of air hiding inside it, called oxygen, a fish can find its air right in the water. But wait — if water keeps going in Sunny's mouth, where does it come out?

Whoosh — out the sides! Leo spotted two little flaps behind Sunny's eyes, opening like tiny doors. Under those flaps live her gills — soft, red, feathery combs. If Leo could see through Sunny's head, he'd watch water slide in her mouth, brush over the red gills, and slip back out — and as it passes, the gills catch the oxygen and send it into her body. Gills grab the air hiding in the water!

Leo watched Sunny's mouth go open, shut, open, shut, never stopping — so she was never holding her breath at all. She was breathing the whole time, just like Leo breathes with his lungs, only her air comes from water instead of sky. And here's a wow: a whale is NOT a fish — it has lungs like Leo, so it must swim all the way up to the top to gulp air, but Sunny never has to!

That night, Leo and his mom tried a trick. They filled a glass with cold water from the tap and left it sitting on the table. After a while — look! Tiny, tiny bubbles stuck to the inside of the glass. That was the hidden air sneaking out of the water. "So THAT'S what Sunny breathes," Leo whispered.

At bedtime, Leo waved goodnight to Sunny. Water in her mouth, water over her red feathery gills, water out the little doors — and the oxygen stays inside to keep her swimming. Leo smiled and said it out loud, and you can say it too: gills grab the air hiding in the water!

Lesson scenes

Good Morning, Sunny

Before school, Leo pressed his nose against the fish tank to say good morning to Sunny the goldfish. Sunny's little mouth went open, shut, open, shut, all the way underwater. Leo puffed out his cheeks — he could only hold his breath a few seconds — so how could Sunny stay under all day and all night?

Air Hiding in the Water

Leo looked closer and saw something surprising: water was flowing right INTO Sunny's open mouth, again and again. She wasn't drinking it — she was breathing it! Water has tiny invisible bits of air hiding inside it, called oxygen, so a fish finds its air right in the water.

Leo's Big Question

But wait, thought Leo. If water keeps going in Sunny's mouth, again and again... where does it come out? Leo leaned in and spotted something behind Sunny's eyes — what do YOU think happens next?

Whoosh — Out the Little Doors!

Whoosh — out the sides! Behind Sunny's eyes, two little flaps open like tiny doors, and under them live her gills — soft, red, feathery combs. Water slides in her mouth, brushes over the red gills, and slips back out — and as it passes, the gills grab the oxygen and send it into her body!

But a Whale Is Not a Fish!

Sunny's mouth goes open, shut, open, shut, never stopping — she breathes the whole time, just like Leo breathes with his lungs, only her air comes from water instead of sky. And here's a wow: a whale is NOT a fish! It has lungs like Leo, so it must swim all the way up to the top to gulp air — but Sunny never has to.

Key takeaways

• Fish do not hold their breath underwater.
• Water has oxygen hidden inside it.
• A fish’s gills grab oxygen as water flows over them.
• Whales are not fish; they have lungs and must come up to breathe air.

Mini quiz

• Where does Sunny find her air?
• What do Sunny's red feathery gills do?
• Which animal must swim all the way up to breathe?

Common questions

Do fish hold their breath underwater?

No. Fish breathe the whole time by moving water over their gills.

What do gills do?

Gills grab oxygen hidden in the water and send it into the fish’s body.

Why does a whale come up to breathe?

A whale has lungs, not gills, so it must swim to the top to gulp air.

Parent or teacher tip

After the lesson, watch a fish’s mouth and gill flaps together and say: “Water in, over the gills, oxygen in!”