I have housed a few gravid (I guess - they are very fat) mosquito fish in a native community tank for well over a month hoping they would bear young. So far I haven't seen any young & all but one are still very fat. I had one I thought had young; I noticed it lost mass, but never saw young. It is likely the young were immediately eaten by others, if there were some born, and the possible mother developed white lips & died.

I wonder if a couple bouts with ick & resulting treatments could have caused fish not to bear young. All remaining females are still very fat & healthy looking.

Is it reasonable to try to maintain a group of mosquito fish as producers of live food in a community tank?

Edit:
Sorry, just saw livebearer group.

I would say both livebearers and egg layers breed much more often than the aquarist thinks. Tankmates consume the eggs and offspring as quickly as they are produced.

Unfortunately for them, the male gambusia were eaten soon after aquarium introduction, so only fat females were left. Therefore, I doubt the females were fertilized after being in my tank. I watch my fish for at least an hour/day, and I've only noticed the one losing mass.

I've heard they can delay giving birth, but I thought this period of time (month & 1/2) very long for a short-lived fish.

Unfortunately for them, the male gambusia were eaten soon after aquarium introduction, so only fat females were left. Therefore, I doubt the females were fertilized after being in my tank. I watch my fish for at least an hour/day, and I've only noticed the one losing mass.

I've heard they can delay giving birth, but I thought this period of time (month & 1/2) very long for a short-lived fish.

Female gambusia can have up to 10 broods from a single mating, so I don't think the fertilization is a problem. Your females will very likely have more broods. Put your biggest, fattest female in a breeding trap. You can buy these at petsmart for pretty cheap. This will help to protect some of the babies. You won't get all of them though, because the female will eat some of them. What are the water conditions(ammonia, nitrites, nitrates, ph)? Females can delay birth for quite a while, and it's mostly due to water conditions not being right. Do you have plants or other cover in the tank? Sometimes females will delay birth if they don't think there are enought hiding places for the young.