my problem with cons is that the size of their fry is miniscule. did you know that a guppy fry is bigger than a midas fry. if you need feeders now, i would go with livebearers.
the best part is that in the 30 gallon tank that you would need for one pair of cons is big enough for 15 platies/mollies, or 30 guppies. then once a fish becomes pregnant, move her into the 10 (not 30) gallon growout. once she has babies, remove her.
somebody said that their livebearers ate most of the fry.
if you use marbles for substrate in the "delivery room" (growout tank) the babies can hide from their mom in the space between the marbles until you notice the little guys. you aren't suppose to leave her in the tank, because in the wild the babies just hide until they are big enough to join the group of mollies/platies/guppies etc. because otherwise they would be eaten be their parents and anybody else who was hungry.