On the outside of the monumental entrance this is what to me seems a dolphin. Fishes (and fish-like animals) represent Christ. I quote from the Wikipedia: "Among the symbols employed by the primitive Christians, that of the fish seems to have ranked first in importance. From monumental sources such as tombs it is known that the symbolic fish was familiar to Christians from the earliest times. The fish was depicted as a Christian symbol in the first decades of the second century. Its popularity among Christians was due principally, it would seem, to the famous acrostic consisting of the initial letters of five Greek words forming the word for fish (Ichthys), which words briefly but clearly described the character of Christ and the claim to worship of believers: Iesous Christos Theou Yios Soter, meaning, Jesus Christ, Son of God, Saviour."
On the other hand it may be a whale, in which case the story of Jonah springs to mind. Back to the Wikipedia: "He was the son of Amittai (meaning 'My Faithfulness'), from the Galilean village of Gath-hepher near Nazareth. God orders Jonah to prophesy to the city of Nineveh. Not wanting to, Jonah tries to avoid God's command by going to Joppa and sailing to Tarshish. A huge storm arises and the sailors, realizing this is no ordinary storm, cast lots and learn that Jonah is to blame. Jonah admits this and states that if he is thrown overboard the storm will cease. The sailors try to get the ship to the shore but in failing feel forced to throw him overboard, at which point the sea calms. Jonah is miraculously saved by being swallowed by a large fish. In chapter two, while in the great fish, Jonah prays to God and asks forgiveness. As a result, God commands the fish to vomit Jonah out."