why are they called " tooth fish " ,do they have teeth ?

Answer 1

I'm not really sure what you're calling a "tooth fish". Do you mean the Antarctic toothfish (ones that have a natural "antifreeze")? http://en.wikipedia.org/wiki/Antarctic_cod Or a toothcarp? http://www.jjphoto.dk/fish_archive/tand1.htm

The antarctic toothfish is a predator that eats other fish, so it does have teeth: http://en.wikipedia.org/wiki/Image:Patagoniantoothfish1.jpg. I wasn't able to find out if this was the reason behind the name, but they are also called Antarctic cod and Chilean sea bass.

You might be surprised to find out that most fish do have teeth of some kind. Some have teeth like we'd normally think of teeth (like a shark or barracuda), but even the little fish in an aquarium have them - more often than not, the teeth are just hardened projections from the roof of the mouth or in the throat. These are called pharyngeal teeth.