Knowing only the inside of a container, they are right at home in an aquarium. Wild caught fish being held in a holding facility in most cases go without eating. Then they are transported usually half way around the world to another holding facility. Then your local store will put in an order, so they are boxed up again. When you visit that store the fish have been exposed to no less than three different foreign environments and are very hungry.
Some fish can survive up to twenty-one days without food but permanant intestinal damage can occur.
This explains why mysterious deaths can happen in a fish that was previously doing well. Finally YOU take it home for it's final acclimation, and hopefully a varied diet to its liking. A captive bred fish is quarantined and observed four days prior to shipping, then shipped overnight. Waiting until right before shipping to stop feeding the fish are also less susceptible to diseases that can be brought on by malnutrition and the lowering of their immune systems. Tank raised fish have been raised on a varied diet of readily available aquarium foods, so there's little or no transition for them.