5. Sharks

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Sharks are fast-swimming fish

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that glide through water at speeds up to 40 miles an hour

Their graceful bodies are built for constant swimming and speed

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Sharks’ skeletons are made of cartilage

A shark’s eyes are on the side of its head, and its mouth is on its underside

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A shark’s body is covered with sharp, tooth-like scales

Shark skin is so rough that it can be used just like sandpaper

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Most fish have a swim bladder

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This is an organ that helps them float

Sharks do not have a swim bladder, instead they have large livers

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The oil in their livers is lighter than water

which helps the shark float

Different sharks have different kinds of teeth

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Sharks that eat fish have sharp, triangular teeth to catch and hold

their slippery prey

Sharks that eat shellfish have broad, flat teeth to crush shells.

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Sharks that eat fish have sharp, triangular teeth to catch and hold

their slippery prey

Sharks that eat shellfish have broad, flat teeth to crush shells

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Some sharks have several rows of teeth which are replaced

every few weeks

Behind the mouth are gill slits

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When sharks swim, water is forced out the gill slits

Most sharks must swim all the time so they can use their gills to breathe

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Sharks use their fins for steering and balance as they swim

Their tail and back fin push them through the water

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