Feed them brine shrimp, blood worms, mosquito larva, midge larva. Pretty much just small aquatic invertebrates. to get a nice ammout of mosquito larva put a bucket full of water in your backyard and in a week or two you will have plenty (i dont know if skeeters are out yet so you may have to wait untill it gets warmer for this to work). You can raise brine shrimp using kits found at alot of petstores and you can find all of the foods i mentioned frozen pretty much at all petstores. I think Elmers sometimes has live blood worms too, but not in large quantities. you may also want to check bait stores and see if they have larger quanties of stuff like blood worms.