Use it for a fry grow out tank, or a feeder grow out tank. Get two more tanks and you will have a feeder farm.
one tank for mating
one tank for birthing (live bearers)
one tank for grow out
you already have a feeder tank.
Oh, you can also section the tank to be your entire feeder farm. But you have large tanks and fish that are getting big appetites. You can start with sectioning it now and then later use it for the birthing tank.