Very good and interesting questions!
When the wicked Haman plotted the genocide of the Jewish People some 2,400 years ago in Persia, he consulted the stars to see which month would be the most propitious to execute his murderous plan. He mistakenly concluded that the month of Adar, whose sign is Dagim (Pisces), which means “fish,” contained no special merit for the Jews. Therefore, he surmised that, just like a fish, he could “swallow” his prey, the Jewish People. The fact that death had “swallowed” Moses on the seventh day of Adar supported his contention.
However, Haman had forgotten two “small” points. One is that Moses was also born on the 7th of Adar, and lived a complete 120 years, to the day, which is a sign of a righteous person. The second point point: while it's true that fish can swallow up their prey, they can also get swallowed up by bigger fish themselves! This is exactly what happened to Haman and his supporters. All their plans were turned upside down, and Haman and his family were hung on the exact same gallows which he had prepared for Mordechai.
This total turnabout of events, from potential tragedy to great happiness, is symbolized by the Pisces sign of two fish swimming in opposite directions. Happy Adar and happy Purim!
