Let us compare the different texts:

Eb3-24 Ab4-19 Ka3-20 Ra6-16 Ra6-17 Cb2-14 Cb2-15

There are at least two parts: 1) a fish with head upwards 2) a 'roof' showing darkness. And in Keiti (E) and Small Washington Tablet (R) one fin is pointing to the left.

As the preceeding glyph (Eb3-23) implies a downward direction and this glyph shows darkness there is a coherence of thought. On the other hand the fish has its head pointing upwards (as in the first half of Mamari's moon calendar), a sign of growing.

The fish is ascending and darkness falls. Sometimes the moon is called a fish. The fin to the left of a fish might be a pointer: the moon arises in the east (to the right as seen from Easter Island) and advances towards the left. Or the fin might show part of the crescent of the moon, in which case the moon is at the western horizon.

Thinking about going up and going down and the roof-sign I realize that there is a type of glyph with the 'roof' turned upside down which I should mention here here.