Mine ate/eat frozen baby brine shrimp just fine. Infusoria (as a generic term) works as well. In fact this is what the fry will survive on for the first several days. It is already present in your aquarium already so you don't have commit energy to cultivating infusoria in larger amounts. (which is pretty easy to do) Unless you are going to be a serious breeder of fish and need a lot of nutrients for a lot of fry, cultivating infusoria isn't necessary.
Stick with your fry food and or frozen baby brine shrimp and you will be fine. You will have large CPDs in no time! Congrats.