Live food is best, fish grow fastest on live food. If the species of fry you have are a neutral pH fish then infusoria is best (it's difficult/impossible to culture infusoria in acidic water). Most of the literature states that infusoria is microscopic and not visible to the naked eye. That's not true. In a stagnant (no filtration/aeration) heavily planted tank exposed to daylight with no fish in there and at a temp of ~80F your naked eye will see living moving swimming & crawling organisms of all sorts after only 10 days. And if your timing is good you can leave it outdoors in the warmer months and you'll get mosquito larvae as well, which when only a few days old are small enough for fry. Once your fry are large enough to eat other fry you can breed one adult well-conditioned pair of Macropodus opercularis under the right conditions every week, and with coordinated timing scoop out the bubble nest with a large spoon while M. opercularis fry are hanging from the nest and feed it to your fry.