I have been trying for a while now to get a colony of native fish started. I'm finally having some success. These are the least killifish (Heterandria Formosa). The smallest livebearer in the world and the smallest fish in North America. I only have one adult female but she is dropping a new fry every few days. I have four fry as of 1 Feb 2020. The adult fish is a little over 1/2 inch long.

 

 Heterandria formosa (known as the least killifish, mosqu or midget livebearer)^[3] is a species of livebearing fish within the family Poeciliidae. This is the same family that includes familiar aquarium fishes such as guppies and mollies. Heterandria formosa is not as commonly kept in aquaria as these species. H. formosa is once one of the smallest fish in the world (7th smallest as of 1991),^[4] and is the smallest fish found in North America.^[5] Despite the common name "least killifish", it belongs to the family Poeciliidae and not to one of the killifish families.

https://en.wikipedia.org/wiki/Heterandria_formosa