And when I say little, I mean LITTLE. Heterandria formosa is the 7th smallest fish in the world, and is the smallest livebearer. The males barely top out at 2cm, the females slightly larger. H. formosa are a United States native with a range from the Cape Fear River drainage in North Carolina to southern Louisiana . I am not sure what locality mine are from though. They are so tiny that the females superfoetation, where the females have kind of a conveyor belt of different embryos and then pop one out every day.
The small colony that I have seem to fit comfortably in a 1 gallon jar on my windowsill, stuffed with plants and a spawn mop. I hope to breed them very similar to the pygmy sunfish that I have. It is wonderful how incredibly small they are :) Hopefully the settle in and I can play around with my macro tube extenders again!
One hilarious thing is that the gonodopodium on the males is enormous compared to their body size. At least it is quite easy to tell who is male and female! Really hope that I can observe some spawning action soon. When the males have brief territorial disputes, the description of "sword fighting" is QUITE literal.