Ideas:

1. The second fish is identical to the first one. Fishes live in water. The water runs downwards. Fishes are found in the underworld. That is the earthly picture. Astronomically seen water is also found down under.

2. The front half of the fish, I believe, is a sign of time zero. The cycle is completed and time stands still for a while before the next cycle starts. If it starts. The indians of Meso-America thought they had to make it start, like a old car where you have to turn the crank.