What is Spanish for fish?

In Spanish, there are two Words for fish. One Word is for a free swimming fish that has yet to be caught. The Word for this one is 'el pez.' The other is the Word for a fish in hand: a caught one. The Word for this one is 'el pescado.' In a Spanish or Mexican restaurant, you always order pescado, not pez. These are just generic Words for generic fish. Spanish also contains many Words for specific species of fish. How well you use these Words (pez/pescado) is a reflection on your Spanish ability.