Freeing animals

One of the most charming traditions in Buddhism I find is setting animals free. Fish in tanks, birds in cages....dogs and cats in pet shops, goats, cows, sheep, horses, chickens ...on farms... Buddhists buy them and set them free. This is to generate good karma. I don't care much about the karma part, but I loooooove the setting free of animals. Is was recommended against depression in children by my teacher at the monastery.