What fish would work in a no-header, Walstad-type nano tank?
I'm thinking plenty of plants and maybe a light. Right now I have a 1.9 gallon with some plants, a beta (going to add more plants), and a small sponge filter. Also planning on starting another low-tech nano, looking into what would happen if I used no heater, and possibly no filter.
Least Killies (which are actually a US native livebearer) are the smallest livebearing fish in the world. I've got a colony in a 5 that's been chugging along. Tons of personality, hardy as frakking heck (I had 11 surviving in 40 degree water last fall before I was able to get them out) and would be ok in small spaces. Males are smaller than females, and have some very entertaining territorial behavior if it's a boys-only tank. Males and females spar on and off, but no one gets hurt. I think of them as the fish version of chihuahuas.
Only thing I've noticed that could be of concern is that males seem to assume that all other fish are both female and willing partners, regardless of species or sex. My male scarlet badis were not pleased.