The fish was an early symbol for Christianity, since the Greek word for fish, ichthus, is an acronym (the first
letter of each word) for the Greek phrase "Iesous Christos Theou Huios Soter" which means
Ἰησοῦς - Iesous - Jesus
Χριστὸς - Christos - Christ
Θεοῦ - Theou - God
Υἱός - Huios - Son
Σωτήρ - Soter - Savior
Complete Meaning is : "Jesus Christ, Son of God, Savior"