Oceans , rivers , and lakes are home to an extraordinary variety of animals . Fish are vertebrates , which means they have a backbone , just like you. But instead of breathing air with lungs , fish breathe using gills . As water flows over the gills , they pull out the oxygen that is dissolved in it, letting the fish breathe without ever coming to the surface .
Fish are beautifully built for life in water . Most have a smooth , streamlined shape that slips easily through the water , fins to steer and push themselves along , and a covering of overlapping scales to protect their bodies . Many also have a special air-filled bag inside called a swim bladder , which they fill or empty to float at just the right depth without sinking or bobbing up.
📷 Joe Mabel (on Flickr as Joe Mabel from Seattle, US) · CC BY-SA 3.0✨ The ocean contains about 3.5 trillion fish across more than 34,000 known species — that's far more species than all land vertebrates combined .
🔗 Match each fish body part to its job.
Helps the fish float at the right depth Protect the fish's body Steer and push the fish through water Take oxygen from the water to breathe
Helps the fish float at the right depth Protect the fish's body Steer and push the fish through water Take oxygen from the water to breathe
Helps the fish float at the right depth Protect the fish's body Steer and push the fish through water Take oxygen from the water to breathe
Helps the fish float at the right depth Protect the fish's body Steer and push the fish through water Take oxygen from the water to breathe
Not every creature in the sea is a fish . Octopuses , squid , crabs , jellyfish , and sea urchins are all invertebrates — animals without a backbone . A jellyfish has no bones , brain , or heart , yet it has drifted in the oceans for hundreds of millions of years . Each of these animals has its own remarkable way of surviving underwater .
📷 JULIAN MASON from London, UK · CC BY 2.0🗂️ Sort each sea creature: fish (has a backbone) or not a fish?
Fish Not a fish
Fish Not a fish
Fish Not a fish
Fish Not a fish
Fish Not a fish
Fish Not a fish
🔗 Match each sea creature to something special about it.
Lives safely among sea anemone stinging tentacles The male carries and hatches the eggs Has eight arms and can change colour instantly Can detect a drop of blood from far away
Lives safely among sea anemone stinging tentacles The male carries and hatches the eggs Has eight arms and can change colour instantly Can detect a drop of blood from far away
Lives safely among sea anemone stinging tentacles The male carries and hatches the eggs Has eight arms and can change colour instantly Can detect a drop of blood from far away
Lives safely among sea anemone stinging tentacles The male carries and hatches the eggs Has eight arms and can change colour instantly Can detect a drop of blood from far away
💡 Coral reefs are sometimes called the rainforests of the sea — they cover less than 1% of the ocean floor but are home to about 25% of all marine species .
The deep ocean is one of the most extreme places on Earth : pitch black , freezing cold , and crushed by enormous pressure from the water above . The fish that live there have astonishing adaptations . Many make their own light using a trick called bioluminescence , glowing to attract prey or to signal to one another. The anglerfish even dangles a glowing lure from its head like a tiny fishing rod to tempt smaller fish straight into its mouth .
📷 Matthew T Rader · CC BY-SA 4.0✨ The whale shark is the largest fish alive , reaching 12 metres — but it feeds only on tiny plankton , which it sieves through its enormous mouth .
✍️ Fill in the sea-life words.
Fish breathe using _____ to get oxygen from the water , and they are _____ because they have a backbone . Some deep-sea fish make their own light using _____ .
gills vertebrates bioluminescence lungs invertebrates
