Hey Conway!
It wasn't unplanned by them! ;)
Just check any morning at first strong light.
My limited experience agrees with Hank's. Our Praecox,
at least in a relatively roomy aquarium, were/are
quite tolerant of fry, if they are well fed. They
could well be called, "the guppies of the
rainbowfish."
I began keeping rainbowfish after keeping killies. I
too tried keeping rainbow fry in small containers, a
la the killinuts. It didn't work for my Madagascars.
(And then my son directed me to the half dozen tiny
Madagascar fry coasting along an inch or two from the
small power filter intake on the parent's 20-gallon
tank.)
Killie are amblers and aquarists get by, raising them
in smaller tanks, though they would be impressed if
they raised the same fry in 20-longs. That isn't
always possible I realize.
But your rainbows are swimmers, not amblers and even
the fry need space. Their mouths are so small (even in
the case of larger looking fry such as the Bedotia)
that they need the tiny powdered fry foods such as
APR, Tetra egglayer or one of the many other new foods
commercially available. I found it useful to set them
up in greenwater tanks, with lots of snails to clean
up the extra powdered foods. They can browse the
protists in the greenwater when not feeding on the
powdered food. The greenwater's photosynthetic
properties may also keep the water a little safer.
Militant and frequent small partial water changes, as
they grow up, doesn't hurt. YMMV
I still transgress in keeping the smaller rainbows in
20s with power filters. Once in a while a larger tank
is available. I would be interested in what others use
for their adult rainbowfish. Hank mentioned dropping a
praecox mop in a rearing tank. How big do people go
with grow out tanks?
Thanks and all the best!
Scott
Park Forest, IL