2. The sun and the stars are 'eternal', not closing their eyes, whereas the moon is closer to us mortals, evidently having a life cycle ending with her death. Though being reborn later again.

In the first half of any life cycle vigour and strength is increasing, thereafter things are going downwards. Therefore, a fish going up (head up) means the time of growing. Focus and interest as a rule is located to the first part in life.

"The five stages of a baby's development are: kaukau, puepe, tahuri, totoro, mahaga. Kaukau = newborn baby's first hand and feet movements (kaukau or kau). Puepue = said of a newborn baby when, a few weeks old, it begins to distinguish people and objects: ku-puepue-á te poki. Tahuri = of a new-born baby, to move from side to side: ku-tahuri-á te poki. Totoro = to crawl; ki totoro te poki, when the baby crawls. Mahaga = baby when able to stand by itself."  (Vanaga)

Another factor which must be considered is the fact that a 'fish' going down always does so in the west, never in the east. But the moon was anciently considered being born in the west and dying in the west, contrary to all other heavenly bodies. Although the moon sometimes was referred to as a hare (or rabbit) she was also often symbolized by a fish in ancient cultures.

Basically the ika glyph type is a rising 'fish'. When we see an upside down (or reversed) glyph in the rongorongo texts - e.g. a sinking 'fish' - it means the opposite of the normal glyph. When moon is in the waning phase she is dying.