I bet they're decapsulated brine shrimp eggs. Look around the internet and you'll find recipes on how to grow them. From what I've seen, it looks pretty simple. And most fish love brine shrimp. Lots of people feed baby brine shrimp to their fry. I do know that if you intend to feed baby brine shrimp to your fish, you will need a baby brine shrimp net. It has a mesh that is fine enough to capture them.
Fry in general, I guess...I wasn't thinking of any in particular, and I am not currently breeding any fish (although I have a 10 gallon that is going to house a breeding colony of something soon...not quite sure what).
LOVE IT! I have a 4 oz pack, feed Adult CPDS, feed tetras, ALL my fish love it! Get some right away. I feed this to get my CPDS in breeding condition, no hatching just a little sprinkle goes a long way!! It really brings out the red in them! I feed the fry too once they get a little bigger. I highly suggest it! Once you try this you'll never go back!!