Hibil's contest with darkness has its prototype in Marduk's battle with chaos, the dragon Tiamat, which (another striking parallel) partially swallows Marduk, just as is related of Hibil and the Manichaean primal man.
Then comes the story of the struggle between the gods of light and the powers of darkness, and the final victory of Merodach, who clove Tiamat asunder, forming the heaven out of one half of her body and the earth out of the other.
This conception of the strife of God with the devil was further interwoven, before its introduction into the Antichrist myth, with another idea of different origin, namely, the myth derived from the Babylonian religion, of the battle of the supreme God (Marduk) with the dragon of chaos (Tiamat), originally a myth of the origin of things which, later perhaps, was changed into an eschatological one, again under Iranian influence?
For the "great fish" is ultimately Tiamat, the dragon of chaos, represented historically by Nebuchadrezzar, by whom for a time God permitted or "appointed" Israel to be swallowed up.
Marduk destroys Tiamat in a similar manner to that in which Daniel destroys the dragon (Delitzsch, Das babylonische Weltschopfung Epos), by driving a storm-wind into the dragon which rends it asunder.