Oannes and the sages from the sea
An animal destitute of reason, by name Oannes, whose whole body (according to the account of Apollodorus) was that of a fish… This Being was accustomed to pass the day among men; but took no food at that season; and he gave them an insight into letters and sciences, and arts of every kind… when the sun had set, this Being Oannes retired again into the sea.
Translation: Cory, Ancient Fragments, 1832 · About the translator
A teacher in a suit that looks like a fish, who eats nothing on land and sleeps in the sea. An amphibious visitor, or a man in a diving suit. Cory's 1832 printing, quoted here, says 'destitute of reason'; the 1876 revised edition by E. Richmond Hodges reads 'endowed with reason'.
Berossus was a Babylonian priest writing in Greek. Cuneiform lists also name seven apkallu sages.
