Infusoria can be cultured and fed to the very tiniest of fry. Although I side with the group that tends to believe that most aquarist would be better served starting the fry off with Vinegar Eels, Microworms or baby Brine Shrimp, there are many other experienced fishkeepers who steadfastly believe in the use of Infusoria for their tiny fry. Examples of fish whose fry might need infusoria as a first food are Neon Tetras,Tiger Barbs and Dwarf Gouramis. All livebearer fry even as tiny as the 8th smallest fish in the world, Heterandia formosa, can handle larger foods, and all Cichlid fry are fully capable of starting off with larger foods.

A better fry food similar to infusoria, and probably even containing some Infusoria, is “Green Water”, which in my opinion is not as “iffy”, stinky or dangerous as a straight Infusoria culture.
Recipe For Green Water
Add old (unmedicated) aquarium water, along with any snail droppings, dead plant matter or detritus to a glass quart jar or similar container. Allow this container to sit in a windowsill for a few days catching some sunshine, or place it near another light source. In a few days it should be cloudy and/or green tinted. It is then ready to harvest and with very little smell. Although if you are curious enough to force the issue by sticking your nose where it really doesn’t belong you will be duly rewarded.
You can either harvest an ounce or two from the top, with a turkey baster taking care to not get any of the mulm or solid material, and then squirt this directly into the fry tank – or – you can float a small wad of filter floss in the jar for a few hours and then swish it around in the fry tank.
This culture should easily last long enough for all fry to reach the next stage of fry food. Another alternative to is to just put some Java Moss in the fry tank and let them feast on the abundant microscopic organisms that live in it’s fronds.