Ever wonder why Chinese businesses often have a big aquarium full of fish? The Mandarin Chinese word for "fish" is yś (魚 / 鱼) which sounds like the word for "abundant" (裕). Flowing water represents a continuous renewal, so an aquarium is a good luck charm which is meant to bring continuous abundance to the establishment.
This means that companies that sell fish and aquariums are virtually recession-proof. A story carried by Reuters reports that demand for aquariums continues even during recessions, because companies are willing to try anything (even superstition) to keep afloat. And if the fish help stimulate business, that's a big incentive to get even more during good times, making the fish vending business profitable during good times and bad.