‘porthole livebearer’
These are a delightfull, small livebearer — mine were roughly the size of Endler’s livebearers and didn’t seem in a hurry to get much bigger.
I remember at the time being unable to photograph the ‘portholes’ which showed up a lot better in person.
I kept a small group in a 5.5 gallon tank with some Najas grass, and fry soon showed up without any effort on my part.