Do you have to actually harvest phytoplankton and zooplankton for feed when the fry are just transitioning off of their yolk sacs?

I thought two buckets of fertile pond water left outside in the semi-sun would be teeming with life if you threw in a little organic fertilizer. I contemplated pouring a cup of that water into the aquarium each day to initially supply enough "feed" for the fry.

[I confess to zero knowledge on this topic. I thought fertile pond water was teeming with life, so any amplifications on this topic would be appreciated.]