as said, you need lots of hiding places, much like guppies. but mosquito fish are better at cannibalizing fry than slow guppies.
Also, the ones I kept had very small broods compared to guppies, and were totally inconsistent about dropping them. It wasn't done at predictable intervals, and not all at the same time. That confused me. They dropped less fry, more often.
Hugely gravid females would ping out a few fry but retain the gravid spot & some belly. then drop a few more relatively soon again. no timing.
In ponds, the fry hang in shallows with thick grass & algae where adults can't go, but spook out quick.
The number of fry I got just weren't worth raising for feeders. It was easier netting them out of the ponds with a really long handled big wide net.
Some mosquito fish populations have IPs, some don't.
If you want to raise feeders, it'd be much faster with convicts.