From Southeast Asia come the Rasboras, members of the Cyprinid family of Carps and Minnows. In this post, I'll demystify keeping members of this beautiful family of fishes.
First, Rasboras are schooling fish, and that is how they are best kept. Though some just form loose aggregations, the majority are happiest and live best in large schools. Rasboras come from heavily vegetated creeks and streams rift with species of Cryptocorynes, thus it stands to reason to furnish the foreground and sides of their tanks with these plants.
Like all Carp, Rasboras have no teeth in their jaws, but they prefer small, soft pellets. Live food like Daphnia, chopped or halved White Worms, Brine Shrimp and insects like wingless Dropsilia species fruit flies given three or four times a week is very beneficial and is key to breeding these fish.
They do best in well-planted aquariums in bright, clear waters with a pH between 6.5 and 7.0 and moderately soft, say a general hardness under 10 degrees. They like temperatures in the mid to upper 70's to 80. Properly kept, all are long-lived, with over 5 years not uncommon.
The word 'Rasbora' was what the fish were called in India. When species were exported from there to the West in the early 20th century, science erected the Rasbora Genus in honor of that native name.

Now some species

Synonymous when the word Rasbora is used is the Harlequin Rasbora, (Trigonostigma heteromorpha).
A native of Sumatra, Thailand and the Malay Peninsula, the Harlequin Rasbora is perhaps the most popular of the family. A golden, silvery fish, adult specimens can have a blush of deep red on its unpaired fins. A deep, black chevron mark covers the posterior half of the fish. Reaching a length of 1 3/4 inches, adult fish have a golden line on the top edge of the mark. The golden mark is visually brighter on the male.
This fish does best in soft and acid water, say pH 6.5 to 6.8 and hardness under 6 ppm. Tanks planted with some well-established, broad-leaved Cryptocorynes are perfect for it, as they lay eggs under the leaves, and the young hide in the exposed roots of Crypts. Floating plants make them feel secure. En masse, a large school of Harlequins is very impressive with their red-golden bodies with that deep black mark.
A similar species is T. espei, which is more slender and can have deeper colors than heteromorpha.

My personal favorite is Rasbora pauciperforata, the Red Line Rasbora.
The common name describes the character of this fish; a brilliant red line, edged with gold and black, bisects it, and divides an olive back from a silvery white belly. The fins are all clear, and the fish is partially transparent.
Reaching a hair over 2 inches, Red Lines prefer to be in large groups in thickly planted tanks. There is occasional play among members, but thus far I haven't spawned these fishes. Otherwise, they are beautiful, quiet fishes; in a dark background and substrated tank equipped with a few floating plants, they are nothing short of stunning.
Like all Rasboras, they will not tolerate excess Nitrate, much less any Ammonia or Nitrite. In a well-planted and established tank with clear, clean water, they are quite hardy. They prefer temps in the mid-70's to 80.

Perhaps the most common Rasbora in shops these days is the Brilliant Rasbora, R. borapetensis.
An electric-yellow borders a black line that divides the fish. In happy surroundings, a blush of deep red colors the tail fin.
A hardy, lively little fish with fins smartly spread, a good-sized group in the planted tank is lovely. Like all Rasboras, Brilliants should be kept with calm tank mates, as they are easily bullied. They very much like to school together in the aquarium.
A lovely fish, and hardy enough for the new Rasbora keeper. I highly recommend them.

A tiny schooler for the planted nano tank is R. maculata of the Malay Peninsula.
Reaching an inch long, Maculata, sometimes known as the Dwarf Rasbora, has a peachy-pink body with an dark black spot surrounded by electric pink. Black and red are at the base of the unpaired fins.
Though they are tiny, they are deceptively hardy. With fins well spread, the fish carries itself with an assurance as if it thinks its much larger than it is. Food, both live and prepared, must be quite small. Like all Rasboras, they should be fed between three and five times a day with small meals, no more than they can consume in under a minute.
As it is so small, tankmates must be chosen with care lest it be eaten.
They breed under Cryptocoryne leaves like Harlequins, but the fry are very, very tiny, and must be fed Infusoria and the smallest of Rotifers when they are free swimming. It will be some time, occasionally up to two weeks, before they can manage baby brine shrimp.

A fish not seen much in shops any more is R. dorsiocellata, the High Spot or Spotted Rasbora.
Simply a bright silver with a metallic silver eye, it is the spot in its dorsal fin that lends to its common name. The spot, at the base of the dorsal fin, is deep black, bordered on the bottom by enameled, somewhat metallic, white. The scales are lightly edged in black. Reaching 1 3/4 inches, the fish can have silver and black on the bottom of the tail fin.
Sexes are told in mature fish by the female's slightly larger size and girth than the males.
A very restful, glittering little fish, quite lovely as a large group in a planted 20 gallon with a dark background planted with darker-leaved plants. Calm tank mates are a must with this species.

Called Scissor-Tails, Rasbora trilineata is the largest common Rasbora and winds up our list.
Reaching an impressive eight inches, trilineata earns its common name by its habit of flexing its tail scissor-like. The look is accentuated by orange and black at the tips of the tail. In healthy specimens, Two thin black lines are the back half of the fish, one in the middle, the other on the bottom of it.
Left alone as the only fish in a suitable-sized planted tank, they will constantly breed, and eat neither eggs nor fry. I kept them in a 75 gallon planted tank that in the mid 70's in temperature, fed them a couple times a day, and basically ignored them. They tank was soon full of adult and juvenile Scissor-Tails, easily seen by their flexing tails.
If not for their size a group of Scissor-Tails would be ideal in a good-sized planted tank. Kept in pairs or trios, however, they are not to be trusted with smaller, easily bullied fish. Keeping Scissors in schools diffuses this aggression.

There are a few species that occasionally turn up in shops, but all can be kept as above. I encourage you to research and seek out these fish, as a properly set up Rasbora tank is a rare thing these days, but can be lovely.

Dave