Have you ever wondered why a fish is relevant to Christianity, indeed a symbol of Christianity when displayed in an appropriate context (on the bumber of a car, a tattoo, etc.,)? The reason is not all that surprising once you know it. 

So, here’s the answer:  first, the Greek word for fish, is ἰχωύσ (/ik•sous/). As it happens, this word can form an acronym from the first letter from each word in Greek phrase Ἰησοῦς Χ̔ριστός, Θεοῦ υἱός, σωτήρ – meaning Jesus Christ, of God [the] Son, savior.

And, there you have it.

Now, go and study