The Glimmerfish was a type of fish native to Alderaan. They were small but incredibly fecund swimmers no longer than a finger, covered with reflective metallic scales. Females would lay hundreds of eggs up and down the shores of Alderaan's canals and rivers. When all the eggs hatched at once, the water became a huge, glittering mass of silvery reflections that sparkled from the sunlight. Swarms of the tiny fish swam along the current towards large bodies of water, where they would grow and live out their lives. When no clouds covered the height of the day, it was possible to see the silvery light from orbit.
To the people of Alderaan, the hatching of millions upon millions of tiny fish was a celebration of life, thus the holiday called the Silver Flow was a celebration of the hatching of these fish.