Kent makes a product called Garlic Xtreme that works well as a food attractant. I've used it to get fish to eat with a fair amount of success over the last few years. It is very concentrated, so I would soak the food in just a few drops of Garlic Xtreme for about 15 minutes and then offer it to the fish. That said, have you actually tried feeding the piranha non live yet? If so, what have you tried? By nature piranhas are scavengers and should readily eat frozen thawed silversides and mice. This would be healthier, as live foods such as goldfish can carry parasites and bacteria. It would be much cheaper as well. Good Luck!