Hemigrammus erythrozonus, the Glowlight Tetra

Hemigrammus erythrozonus (Glowlight Tetra). Erythro does mean "red," but the brilliant eyelight and body bar of a Glowlight Tetra can vary from clear bright red to the pink of highly-polished new-minted pure copper. Otherwise, the fish is a fairly translucent brownish, with a silvery white belly. There's a red leading edge to the base of the dorsal fin. Peat filtration and a dark woody background bring out the touches of icy white at the leading edges and tips of fins. The fishes max out at about an inch and three-quarters, with females notably more robust. What small mouths they have. 
 
These beauties were first noticed in a temporary overflow pool in the floodbottom of the Rio Mazaruni, in Guyana (then British Guiana). H. erythrozonus are also found in the Potaro and the Essequibo rivers; in other words they're well-distributed through the central watersheds of Guyana. They were formally published to science in 1909, but they didn't get exported until 1933.
 
Glowlights for the market are all bred now in Singapore. Spawning doesn't quite follow standard tetra procedure, in that the male performs an enticing courting dance for the female, blocking her movements to give her shimmying broadside displays. If she's ready to accept him, their excited fin-flicking movements will build to a climactic side-to-side barrel roll in which about a dozen eggs get extruded in a burst. The eggs will be eaten as soon as spawning heat has cooled, so be prepared to remove the pair. A good trick is to provide a removable screen divider, with plenty of Java Moss all on the breeders' side, where the slightly tacky eggs will stick. With the divider, you can separate the pair for a day or two beforehand, and then screen them from their eggs caught up in the moss afterwards. Though Glowlights will even spawn in water with a pH slightly above neutral, they have a reputation for not being very forthcoming about spawning. They mature early and spawn only while they're young. In my soft water, flirting pairs form even in a planted community aquarium, so I think the problem of reluctance to spawn may be in the hardness of the water. When I'm told that the extremely tiny eggs will swell once they're out in open water, I'm reminded that the water has a lower molarity than the fluids in the fishes' ovary. So it occurs to me that reports of hard water reducing fertility of spawnings might have some connection to impaired osmotic reaction of the egg membrane when water is not very soft. If your Glowlights are resisting spawning, see whether you might encourage them by doing a partial water change with some distilled water.
 
Within a month of hatching, well-fed fry will start to show iridescence. They look like a cloud of sparks, if you can have them against a dark woody background. Animal researcher Grant E Brown and his co-workers have been investigating Glowlight Tetras' reaction to the alarm pheromones that tetras exude when they are attacked or harmed. The effects of an unidentified characoid "fright substance" (Shreckstoff) have been recognized for decades, but recently the actual molecule has been tentatively identified. Alarm pheromones are produced by all Ostariophysii, the giant group of fishes that includes catfishes as well as tetras. In a series of experiments starting in the 1990s, the researchers showed that H. erythrozonus even detected the fright substance exuded from predatory Cichlasoma that had recently dined on tetras. Their alarm responses included increased shoaling, more restricted cruising the tank, more hesitancy about approaching to inspect the cichlid.  "Fin-flicking" is another alarm response": if you know Glowlights and some other tetras, you'll recognize the action of "fin-flicking," but you probably didn't identify it as an alarm display to alert other Glowlights— nor did you imagine that the twitching gesture had some deterrent effect on potential predators. If fin-flickings are important communicating gestures, that would give a purpose to the leading edges of Glowlight fins being heightened with white (see the abstract of Grant Brown's article "Fin-flicking behavior"). 
 
Links. Species profile of Hemigrammus erythrozonus at Tropical Fish Hobbyist. Hemigrammus erythrozonus at FishBase.  Hemigrammus erythrozonus at Wikipedia.