Iconography of Deities and Demons (IDD).
“Mesopotamian semi-divine figure. A Babylonian tradition related by Berossos in the 3rd cent. (BURSTEIN 1978: 13f) describes a creature called Oannes that rose up out of the Red Sea in the first year of man’s history. His entire body was that of a fish, but he had another head, presumably human, and feet like a man as well as a fish tail.
He taught men to write, as well as many other arts, crafts, and institutions of civilization. He taught them to build cities and temples, to have laws, to till the land, and to harvest crops. At sunset he returned to the sea. Later there were other similar creatures who appeared on the earth. These were the sages.
The sage Adapa, a priest of Eridu created by the god Ea/Enki, was also called Oannes. The name Oannes was thus connected, by true or false etymology, with the common noun for a sage in early Akkadian ummiānum, later ummânum.
The other Akkadian term for a sage, apkallu, can also mean a type of priest or exorcist. According to a Sumerian temple hymn, the seven sages came from Eridu, the first city in the Sumerian King List. Since Eridu was the city of Ea who lived in the Apsu, iconography involving water and fish is to be expected for the sages. According to late Assyrian and Babylonian texts, legendary kings were credited early on with having sages.
The Epic of Erra and Ishum (probably 8th cent.) attributes to Marduk the banishing of the sages down to the Apsu, and not allowing them to return. He describes them as pure purādu-fish, perhaps carp, who like their master Ea are especially clever, and were put among mortals before their banishment.
The ritual text bīt mēseri, for encircling a house with protective magical figurines, gives names to the sages of some famous kings in various cities (REINER 1961; BORGER 1974; see also HUNGER 1983: nos. 8- 11). Some of those sages angered the gods.
Ziusudra, also known as Utnapishtim and Atrahasis, was probably the last sage before the flood, the event which marks the division between immortal and mortal sages. Later sages were part mortal, part divine.
Kings credited with a sage include Enmerkar, Shulgi, Enlil-bani of Isin, Hammurabi, Nebuchadnezzar I, Sennacherib, and Esarhaddon, but this time span (legendary/Early Dynastic [26th cent.] to mid 7th cent.) does not match that of the identified iconography.
Certain texts are attributed to sages, notably two medical texts and a hymn (REINER 1961), the Myth of Etana, the Sumerian Tale of Three Ox-drivers, the Babylonian Theodicy, and the astrological series UD.SAR Anum Enlila.
In Assyrian tradition the sages guarded the Tablet of Destinies for the god Nabu, patron of scribes. This information gives a possible link with the composite monsters in the tradition of the Babylonian Epic of Creation, which centers on control of the Tablet of Destinies.
Such a link would explain the scene that puts phenotype 1 (see § II.1) with composite monsters who fight as archers (24), and phenotype 2 (see § II.2) with mermen (44*, 51) and composite monsters (50*). However, in known versions of the Epic, the hero-god, not the composite monsters, is called a sage; thus the relationship is not clear.”
Stephanie Dalley, “Apkallu,” Iconography of Deities and Demons in the Ancient Near East (IDD), Swiss National Science Foundation, University of Zurich, 2011 (text updated 2011 and illustrations updated 2007), p. 1/7.