info needed for fry care in the the great white north Z3/4 -long

Background info first
Pond is 24 x 15 x 3.5(sloping sides). We usually just leave the
"spitter" going to keep a small area ice free, the rest freezes to a
depth of 12". Snow is usually somewhere between 2-3' deep from Dec to
Mar. Temps can get as low as -38c(-36f), but generally stay around
-25c(-14f) or so. Until this year we would just sink plants that are
not able to withstand freezing(iris and a few floating lilies) and the
fish and frogs were on their own. Now the fish are nothing fancy just
a few "feeders" and a couple of Shubumkin that were thrown in to
provide colour . They are now 3 years old 4-6" long with gorgeous
colour and this year have produced a LARGE number of fry, much more
than usual. The thing is, I think even the Shubumkin reproduced this
year and I would like to try and overwinter these guys inside. I have
a few tanks of various sizes but am unsure as to ratio of fry to water
and also as to whether I need to heat or not. The fry are only 1" long
so not large at all and as the pond never reached much more than
21c(70f) according to the floating thermometre, I am unsure how to
proceed. Any information you can provide would be greatly appreciated.

Thanks Elaine