The title of this post is a little misleading. While in theory these little guys are in a bucket, what you're actually seeing here is 20,000 freshly hatched cut bow trout (a hybrid between a cutthroat and a rainbow) in what's called an egg jar.
This is where the little guys get blown around in freshwater at the hatchery before being let loose inside in small raceways when they get a little bigger and have consumed their egg sacs. After that, they are transferred outside and fed until they're ready to be stocked in a river or lake. I found watching them to be pretty mesmerizing. I hope you do too.