The 25,000 known species of fish are divided into three main groups.  They are the jawless, the cartilaginous (KAR-ti-LAJ-i-nus) and the bony fish.  Jawless fish are the last survivors of the world's first vertebrate (VUR-ta-bret) animals, which means "back-boned".  They lack both scales and jaws.  Dating from over 5000 million years ago, only the hagfish and lampreys remain. 

Cartilaginous fish developed about 100 million years later, ancestors of today's sharks.  The skeleton of these fish is made of cartilage (KART-laj), which is not as hard as bone.  These fish have jaws, as well as teeth which are usually hard and sharp.  Their bodies are covered with hard scales. 

Bony fish—fish with bony skeletons—appeared at the same time as cartilaginous fish.  They are the largest group, with about 20,000 species. These fish have an organ called a swim bladder which gives the animal buoyancy (BOY-en-see), the ability to float. 

All fish live in water and breathe with gills.  Fish are cold-blooded, which means their internal body temperature changes as the surrounding temperature changes. 



Fast Fish Facts: 



All fish have a backbone.

All fish are cold-blooded.

There are three classes of fish:  jawless, cartilaginous, and bony..

Fish have been around for 500 million years.

There are about 25,000 different species of fish alive today.

There are about 20,000 different species of bony fish alive today.


Fish Diversity


Fish are divided up into groups of related animals, called Classes.  Below you'll find the name of these classes and some examples.











Myxini (mik-SY-ny)



Chondrichthyes (kon-DRIK-thi-es)

sharks, skates, rays, ratfishes



Osteichthyes (OS-te-IK-the-es)  
      Arctic Charr

bony fish, including lungfishes, lobe-finned fishes, and ray-finned fishes



FISH VERSE (Grades 4-7 and older)


Memorizing facts and figures can help us learn about animals, but so can poetry.  A poem is an organized way of expressing insight through language, and it reveals something more than is said directly.  For example, here are two descriptions of the same animal.  Can you guess which one?

1) A scaly. legless. sometimes venomous reptile of the suborder Serpenttes, having a long, tapering, cylindrical body.

The American Heritage Dictionary


The grass divides as with a comb,
A spotted shaft is seen,
And the it closes at your feet,
And opens further on.

Have passed, I thought, a whip-lash,
Unbraiding in the sun,
When, stooping to secure it,
It wrinkled, and was gone.

I never met this fellow,
Attended or alone,
Without a tighter breathing,
And zero at the bone.

Emily Dickinson (1830-1886)

Could you tell from each description that the animal is a snake?  The first description is factual, but the poem suggests something about how the snake moves, and its effect on us.

Everyone can be a poet, at least to some extent.  Write a poem about how it might feel to be a fish.  Your poem doesn't have to be long, or even rhyme.  Close your eyes.  Can you imagine what it would feel like to be a fish?  What kind of fish are you?  Do you live in the ocean or in a stream?  Is the water cold or warm?  How do plants and other animals look to you?  What does it feel like to travel under water? 

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