Feeding live food will make your fish more aggressive towards other fish if you ever wanted to have tankmates, as dead foods will not do this. But all the previous posts are correct stating about the transfer of disease and such. Just make sure that you know the best DIET for any fish is a VARIED diet. So knowing this frozen and prepared foods should make up most of the diet and Live can be given as treats, also to give your fish exercise and allow it to hunt. Just make sure if you are not breeding the live fish then you are QT'ing them b4 you give them to your fish.