Fry should be fed as many small meals per day as possible, I would often do 4 or 5, feedings on grow out tanks, and allow algae to grow in those fry tanks to provide in between meal grazing. In nature multispinossa spawn on flooded grasslands in Costa Rica, so fry have a constant supply of algae, detritus insect larvae and other stuff to eat.
Below are 1" multispinossa fry, maybe 2 months old.
At the above stage, probably still too small to be acceptable to LFSs.
They may need to be more like the size below, As Tom said, actually recognizable as species, and sellable, about two months older than the 1st pic.
Beside multiple meals, you may need to do daily water changes on the grow out tank, to promote growth, and keep water quality high enough to keep them healthy.
