It depends on your setup. If they are in a tank with an established sponge filter, I would not rush to feed as there is plenty of microscopic food on the filter for them to eat. If you have them in a breeder trap, i would feed them SMALL amounts about 5x aday. If you have frozen baby brine shrimp that is great, if not powered flake food will do. You can order decapped brine shrimp eggs, they do not hatch, you feed them as is. I use this all the time in my guppy tanks with great success. kensfish.com selles it along with other very good fry food. Send Ken an email and he will help you.
Good luck.