When adding a new fish to the aquarium, it is very important that it eats within a day or two. Most fish spend a great deal of time in transit, often going from collector to wholesaler to fish store in a few days. During that time, they are far to stressed to eat usually, and may even require some time to acclimate before getting comfortable enough to eat. For this reason, it is also not always wise to buy a fish the same day it shows up at the fish store. Let the fish acclimate to captive life for a few days and make sure it eats before you have it bagged up and placed into another new environment.