Oannes is a fertility deity from the mythology of Babylon, Chaldea and Phoenicia. The appearance of Oannes is part fish part human he lived among the humans during the day, and at night he would vanish into the sea. Oannes god of wisdom was credit with the revelation of the arts of agriculture, healing and writing. Every night and each year at the winter solstice Oannes was swallowed by the monster Tiamat. Oannes reappeared each morning and each spring.
John and Caitlin Matthews, The Element Encyclopaedia of Magical Creatures, 2013, Oannes, p 351