Badis ruber ("Badis badis burmanicus"). Badis ruber ("ROO-ber" not rubber as I often see) is recently re-established as a senior synonym for the more familiar designation of this fish as a sub-species, B. badis burmanicus. The "Burma Badis" occurs in southern Burma and also in the mid reaches of the Mekong, both on the Thai side and the Laos side, always in slow-moving creeks and streams and weedy ditches.
Recognizably distinct from other Badis by the large dark blotch on the caudal peduncle, this little fish maxes out at 8cm/3 in. The Red Badis appeared in German aquariums in the 1960s, but I'd never seen it in the US until the turn of the new century. In 2002 Sven Kullander and Ralf Britz revised the family Badidae, with a new genus, Dario, that they erected for three minute Badid species, including Dario dario, that are among the smallest Perch-like fishes known, and ten new Badis species. There's an abstract of their follow-up article (2004), in which they were joined by Lukas Rüber.
Dave Sanchez, who started a Badis research group, firstname.lastname@example.org, in Jan 2002, originally as a spinoff from the Apisto Study Group, has had Badis ruber breeding in a community, taking up residences in PVC pipe. When the young have absorbed their yolksacs and are clearly showing their eyes, he's siphoned them out and raised them in plastic shoeboxes, like killies, with strands of Java Moss, a technique he calls a "very simple and very prolific way to get a whole lot of these guys real quick."
Links. An article on Badis ruber is at Seriously Fish, and there's an illustrated species listing on Badis ruber at Tropical Fishkeeping. Alexander A. Priest's article "Badis ruber, a small fish with a big attitude" is archived at the Federated American Aquarium Societies site.
Badis ruber at FishBase. IUCN red list, of "Least Concern".