Most, nearly all, killies can take freshly hatched brine
shrimp after hatching, but a few require infusioria, which,
fortunately, is very easy to culture. Green organisms (euglena, volvox, even algae) is a very important food for early fry development and it's been repeatedly shown in lab studies with lots of anecdotal evidence that fry that get "greens" grow faster and larger than without them.