Why is the fish often used as a symbol of Christ? In the United States, you've probably seen it.  Many Christians like to put a fish on their cars to show their faith.

What is the origin of this symbol?
The fish or "Ikthyus" is Greek, is a very ancient symbol.  In addition to the obvious parallels with Jesus commissioning the disciples as "fishers of men," there was another reason for using the fish.

The phrase -

Jesus
Christ
God('s)
Son
Savior

is in Greek

Ίησοῦς 
Χριστός, 
Θεοῦ 
Υἱός, 
Σωτήρ

ΊΧΘΥΣ (the first letter of each word, pronounced 'Ikthyus') also means fish.