Much of the following text was taken from http://orthodoxpost.com/the-icon-of-the-theophany-an-explanation/
Thus speaks the Lord to Saint John: Come on Prophet, baptize me, even though I am your Creator and the one who illuminates and purifies the universe; touch my divine head, without hesitating. Prophet, allow it for now, I came to accomplish all justice. Truly, do not hesitate because I came to annihilate the hostile prince of darkness who hides in the waters, to free from his nets the entire world (Byzantine Prayer of the 6th hour in the Royal Hours on the 5th of January).
On the sixth of January we celebrate the Baptism of Our Lord Jesus Christ in the Byzantine rite, also called the Theophany. In the first part of this article we will explain to you briefly some aspects of the Feast, in the second part we will enlighten parts of the symbolism of the Feast’s icon.
A . Some aspects of the feast of the theophany (or Baptism of Our Lord)
Theophany stands for showing or appearance of deity. At the age of 30 (the age of maturity for Hebrews), the Savior Christ begins his earthly mission, which is the salvation of mankind enslaved by sin, at his Baptism.
He goes to be baptized with the baptism of repentance, He Who is sinless and God Himself – the Spring of all purity and holiness goes from Galilee to the Jordan to John, to be baptized by him. John would have prevented him, saying, "I need to be baptized by you, and do you come to me?" But Jesus answered him, "Let it be so now, for thus it is fitting for us to fulfill all righteousness." Then he consented. (Mat 3:13-15).
The eternal and beloved Son of God, by entering the Jordan waters, enters inside His own creation, itself subjected to corruption through man’s fall, in order to exorcize it of all the demonic powers and to sanctify it. The world’s sanctification begins, therefore, through the sanctification of the water that Christ performs at His Own Baptism and through the Baptism “with Spirit and fire” that He gives. (cf. Matt 3:11).
B. The theophany icon
In those days Jesus came from Nazareth of Galilee and was baptized by John in the Jordan. And when he came up out of the water, immediately he saw the heavens being torn open and the Spirit descending on him like a dove. And a voice came from heaven, "You are my beloved Son; with you I am well pleased (Mar 1:9-11).
This is the iconographic depiction of the heavenly realm, it represents the heavens opened. The white dove surrounded by a circular boundary depicts the Holy Spirit, Who appears at the time of the Lord’s Baptism.
Jesus Christ Our Lord is shown standing, in the middle of the Jordan River, as in a “flowing tomb” which engulfs Him on all sides, emphasizing that He was immersed as a sign of His burial, because Baptism signifies the Lord’s death.“Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life. (Rom 6:3-4)
Christ the Savior is shown either naked, or having a cover around His hips. Older icons portray Him with no clothes at all emphasizing the Divine Economy of His Incarnation: “(...) Jordan River, tell us do: What did you see and were amazed? I saw naked Him whom none can see, and shuddered in fear. And how was I not to shudder at Him and be frightened? The Angels, when they saw Him also shuddered in awe. And heaven was astonished, and astounded was earth. (...) For Christ appeared in the River Jordan, to sanctify the waters. “ (Kathisma 2, the Feast Orthros).
Saint John the Baptist is shown on the shore of the river, at the right of Christ, stepping firmly toward Him. At the same time he bows showing obedience and reverence toward the One Whom he is not “worthy to untie His Sandals”.
With the right hand above the Head of the Savior, St. John expresses the turmoil that overwhelmed him: “The Baptist became all trembling, and cried aloud, saying: How shall the candlestick illumine the light? How shall a slave lay hands upon his Lord? Sanctify Thou me and these waters, O Saviour, who takest away the sins of the world.” (Hymn from the Blessing of the Waters)
At the bottom of the icon, at the feet of St. John, a shrub is represented with an axe at its root. The meaning is fearfully sobering, teaching each newly baptized : “And even now the axe is laid to the root of the trees; therefore every tree which produces not good fruit is cut down and cast into the fire” (Matt 3:10)
angelic hosts were the unseen witnesses of the Lord’s life on Earth, and were longing to grasp the understanding of the “mystery kept secret since the world began” (Rom 10:25); It was revealed to them (the prophets of the Old Testament) that they were serving not themselves but you, in the things that have now been announced to you through those who preached the good news to you by the Holy Spirit sent from heaven, things into which angels long to look. (1Pe 1:12)
The strange little creatures riding fish at the bottom represent the Jordan River and the Sea (cf. Psalm 114), both fleeing at the sight of something much bigger and greater than themselves entering the water.
Let' s take a closer look at Psalm 114: When Israel went out from Egypt, the house of Jacob from a people of strange language, Judah became his sanctuary, Israel his dominion. The sea looked and fled [referring to the passage of the chosen people walking through the Red Sea]; Jordan turned back [referring to the passage of the chosen people passing through the Jordan River, making their way into the Promised Land] .