Why do Chinese restaurants often have a fish tank?

The original reason for the fish tank was to store live fish prior to cooking. The customer could select the fish she/he wished to eat and it would be removed from the tank and prepared fresh. Most Chinese restaurants do not follow this custom anymore, but stock the tanks with decorative fish.

Fish are very important to the Chinese symbolically. They think it is good luck to have live fish around, plus it is good feng shui to place water in certain places. Fish can mean prosperity and luck, plus the Chinese word for fish, yu, sounds like the word for riches or abundance, all good symbols for a prosperous happy restaurant and a good dining experience for the people.