Puntius nigrofasciatus, Sri Lanka's Black Ruby Barb

Puntius nigrofasciatus (Black Ruby Barb). Black Rubies originally came from Sri Lanka, where the IUCN Red List, 2007, continued to list the species as "vulnerable."  Sri Lankan law technically prohibits their export, but there isn't much official control. According to recent surveys though, P. nigrofasciatus is common enough, within its restricted natural habitats in cool shaded Sri Lankan forest pools and streams over sandy bottoms, where it  feeds on algae and detritus and spawns among weeds in the shallow margins. And wild-collecting pressures are lower now, because all the Black Rubies you'll see on the market are captive-bred.
 
According to a report and official recommendation made by Jonathan Mee,  Sri Lanka's fishes are collected by local village collectors, or casually farmed by farmers, who range from household groups up to the half-dozen big fish producers who control the export trade. Sri Lanka's fishes have formerly been exported to Singapore, then re-exported, but in the new century direct exports of aquarium fishes have been developed.
 
In the bare tank at your LFS and in many photographs you'll see posted, Black Ruby Barbs are undistinguished-looking fishes that will suffer from comparison with the snappier Tiger Barbs in a nearby tank. Their body color is less silvery, and their transverse markings, blackish wedges with ragged edges (nigrofasciatus means "black-banded")  are less crisp. 
 
 
 
Once you have them settled and in good condition, though, a transformation occurs. Now Black Rubies will truly deserve their name: the males' color at breeding time darkens to a deep fiery cherry red overlaid with black, with a bright cherry head. Competing males display flank to flank and head to tail, then start chasing each others' tails until the two are spinning in the water, in an action some biologists call "carouseling." The breeding colors come and go with this species —  a water change may spark them—  but even outside spawning time it's easy to sex them: the slightly larger and more robust females just have black bases to their vertical fins, the males show a strong black dorsal fin and a reddish tinge in their anal fin.
 
Links. Illustrations at a  good brief entry on Puntius nigrofasciatus at AquaWorld  give an impression of the males' rich coloring. There's a species profile of Puntius nigrofasciatus at Tropical Fish Hobbyist. 
 
 
Puntius nigrofasciatus at FishBase. Puntius nigrofasciatus at Wikipedia.