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.
Now "Pethia nigrofasciata". For many decades close relationships within "Puntius" in the usual broad sense have been detected among "P." stoliczkanus, "P." conchonius, "P." phutunio, "P." cumingi and "P." nigrofasciatus. In June 2012 Rohan Pethiyagoda and co-workers, in a synoptic study of South Asian (Indian and Sri Lankan) ''Puntius" species, in that familiar broad sense, found five separate lineages, within which they identified three separate new species: our familiar Puntius nigrofasciatus, serving as type species of the new genus Pethia, becomes Pethia nigrofasciata. Pethia (it's feminine) is the Sinhala word for small cyprinids in general, "minnows"; that it chimes with Pethiyagoda's name isn't officially noticed.
The new species has been identified through shared genetic markers (stretches of mitochondrial ribosomal RNA and cytochrome b); some minute but unique shared skeletal features; and in surficial morphology, a stiff (ossified) last unbranched dorsal ray with serrated, not smooth edge, the absence or rudimentary presence of maxillary barbels, the black blotch on the caudal peduncle (where the body narrows just before the tail fin) and frequently other dark blotches or bands on the body.
The evidence marshalled by Pethiyagoda and team looks convincing, but we'll have to see what the professional reaction will be.
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.