Fish are ectotherms that have many adaptations that allow them to live in water including gills, fins and scales.

• Fish are categorized into three classes:
  • Jawless Fish like eels have round mouths and long, tubelike bodies covered with slimy skin and no scales. Their flexible bodies are made of cartilage (the stuff your ears and the tip of your nose is made of)
  • Cartilaginous Fish include sharks, skates and rays. This group is similar to jawless fish except that they have moveable jaws and scales.
  • Bony Fish such as the goldfish in your aquarium have skeletons made of bone. About 95% of all species of fish belong to this class.

There are more than 30,000 different species of fish - more than all other species of vertebrates!

In fact, the number of fish in the sea is greater than the world's population of amphibians, birds, mammals and reptiles added together!