just stop feeding them live, it is seriously that easy... natts at that size will eat just about anything when they are hungry, but they will eat live just about anytime they see it. if they aren't eating shrimp or whatever you are feeding them, just keep trying until they realize that it's food, it may take a day or so, but once they put it all together, they'll start attacking it right when it goes into the water. just make sure you do not cave in and give them feeders, you need to completely eliminate them from their diet if you want the best chance at being successful in introducing other foods. as far as veggies go, i know alot of people feed their piranhas peas and little pieces of carrot.