Classic Car Intelligence
  • Species: Boraras merah

  • Species: Boraras urophthalmoides

  • Species: Rasbora pauciperforata

  • Species: Rasbora einthovenii

  • Species: Rasbora elegans

  • Species: Trigonostigma espei

  • Species: Rasbora hengeli

  • Species: Trigonostigma heteromorpha

  • Species: Rasbora trilineata

  • Species: Rasbora borapetensis

  • Species: Trigonostigma espei

  • Species: Boraras merah

  • Species: Boraras urophthalmoides

  • Species: Rasbora pauciperforata

  • Species: Rasbora einthovenii

  • Species: Rasbora borapetensis

Asian beauties: the Rasboras

13 January 2017


The rasboras are a small group of Asian cyprinids that have been popular among aquarists for decades thanks to their attractive colours, small size, and peaceful disposition. Most make excellent community fish, showing little of the tendency to harass other fish that some of the barbs and tetras occasionally exhibit. The best known species is the harlequin rasbora Trigonostigma heteromorpha but over the years a steadily increasing variety of species has appeared on the market, the latest of which, Microrasbora sp. ‘Galaxy’, has created something of a stir in the hobby, being one of the most attractive new freshwater fish to appear in years. Other popular rasboras include the glowlight (or redline) rasbora Rasbora pauciperforata and the brilliant rasbora Rasbora einthovenii.

General care

Most rasboras are found in forest streams in Southeast Asia, in particular on the Malayan peninsula and much of Indonesia, but at least one species, Rasbora gerlachi, comes from Africa. They are found in both still and gently flowing waters, but almost always the water is soft and acidic, and frequently stained with tannins from decaying wood and vegetation. All feed on small invertebrates and zooplankton. Basic care is generally simple as long as the proper water conditions are provided and overly aggressive tankmates are avoided. Water with a pH around 6.0 and a hardness below 10 degrees GH suits most species well, though the more robust species have been kept in hard, alkaline water without difficult. As with other fish adapted to softwater conditions though, they will not breed in hardwater and their health is often compromised over the long term.

Regardless of the water chemistry, water quality needs to be excellent as these fish notably less tolerant of immature aquaria than their close relations, the danios. Given their small size, potentially predatory tankmates, such as angelfish, should be avoided. In fact most rasboras do best when combined with gentle species of similar size that require the same soft and acidic water conditions. In the case of the smaller rasboras, ideal companions would include checkerboard cichlids, small gouramis, Corydoras, neons tetras, and hatchetfish. Larger species work well with the gentle barbs, pearl and lace gouramis, and placid catfish such as plecs and Brochis. Rasboras enjoy all the standard aquarium foods including flake, bloodworms, and brine shrimps. At least some species eat algae in the wild, so the addition of chopped spinach or an algae-based flake food is a good idea, particularly if you want your fish to show their best colours.

The bright colours of rasboras can all but disappear when kept under the wrong conditions, and in tropical fish shops these fish can look rather dull. Don’t keep these fish in a tank with bright lights or a pale substrate such as silica sand. Instead, keep them in a tank with subdued illumination (or at least lots of shade provided by floating plants) and a dark substrate such as black sand. Judicious addition of blackwater extract to the water or the use of peat granulate in the filter will help to stain the water. The darker the conditions in the aquarium, the more vivid your rasboras will become. Like other colourful fish, their colours are subdued under bright conditions but enhanced where the water is murky or dark. Obviously the use of low levels of light and blackwater extract makes the addition of plants to the rasbora aquarium somewhat difficult, but Java fern, Java moss, Anubias spp., and Cryptocoryne spp. will all tolerate such conditions well.

Rasboras are quite easily spawned in very soft (1-3 degrees GH), acidic (pH 5.0-5.5) water. Filtration through peat is essential. Once the fish are conditioned, the adults should be placed in a tank with warm (around 28C) water decorated with a few plants. Some species, such as harlequin rasboras, lay their eggs on leaves, while others, like the brilliant rasbora, are egg-scatterers. The eggs hatch within one to days, and the rather small fry need infusoria or liquid fry food for their first meal.

Old favourites

The ‘common’ rasbora in the hobby can be one of two different species, Trigonostigma espei and Trigonostigma heteromorpha. Both are relatively deep-bodied fish that get to about 4 cm in length. Their basic colour is coppery with reddish fins, but their most eye-catching feature is the prominent black mark on the flank. This runs from about halfway along the body to the base of the tail, being widest at the front and tapering to a point at the tail. Around the edges the copper colouration is very intense, almost glowing in its brilliance. Trigonostigma heteromorpha is sometimes known as the harlequin rasbora, but it isn’t uncommon for batches of Trigonostigma espei to be sold under that name as well, prompting an alternative name for that species, the false harlequin rasbora. Distinguishing the two is tricky, but the wedge-shaped marks on the flanks usually provide a reliable clue. On Trigonostigma espei the width of the mark narrows very rapidly so that it has an almost L-shaped appearance. By contrast, on Trigonostigma heteromorpha the mark narrows much more gradually, giving it a more triangular shape. Fortunately for the aquarist, care of the two species is identical. These are wonderfully peaceful fish that form schools and should be kept in reasonably large groups (at least half a dozen, but ideally ten or more). A decent sized group of these fish puts on a lovely show, especially in a thickly planted tank with subdued lighting and peat-stained water. They do not mix well with boisterous tankmates though, and under such circumstances tend to pine away.

Trigonostigma hengeli is another species that can be easily confused with Trigonostigma heteromorpha. Known in the trade as the slender harlequin rasbora, this fish has a similar, albeit slightly less deep, body shape and a wedge shaped mark on the flanks. Compared with Trigonostigma heteromorpha, this mark has only a very shallow vertical segment so that the basic shape of the mark is of a longitudinal band with a small triangular blob at the front. Care is identical to that of the Trigonostigma heteromorpha.

The brilliant or black-line rasbora Rasbora einthovenii is a striking species that well lives up to its name. A bit bigger than the harlequin rasbora, it gets to about 8 cm or so in length and has a slender, silvery body covered with rather large, shimmering scales. A black line runs the full length of the fish from the nose, through the eye, and along the flank onto the tail fin. Its fins are basically transparent but with a yellowy tinge and blue-white edges. In terms of care they are not demanding, but they do appreciate clean water with a moderate current and plenty of swimming space. They are good jumpers, though floating plants will help to make them feel more secure.

The two-spot rasbora Rasbora elegans is a real old-timer in the hobby, having been around since the turn of the last century, and with good reason: this is a sturdy, attractive fish that works very well in large community tanks. As its name suggests, this fish has two black spots, one about halfway along the body and another at the caudal peduncle. Otherwise, the fish is shiny greenish-silver. Getting to about 20 cm in length it is among the largest rasboras and needs to be given a tank with plenty of swimming space and a reasonably strong water current. It is an excellent schooling fish for communities containing medium-sized, non-predatory tankmates such as the larger gouramis, plecs, and non-territorial cichlids.

Similar to the two-spot rasbora but not quite so big, the 10 cm long clown rasbora Rasbora kalochroma, has an overall pinkish colour offset by two black spots, one a short distance behind the gill covers and another about halfway along the body. A peculiarity of this fish is its social behaviour: unlike others of the genus, it is not a schooling fish, with each fish in the group tending to claim small territories that they defend against the others.

A small but vividly coloured rasbora is the red-tail or magnificent rasbora Rasbora borapetensis. As its common names suggest, this is a very eye-catching species, with a red tail and black and gold stripes running along the midline of the fish. The overall colour of the fish is silvery-green. This species reaches a length of around 5 cm and should be kept in groups. Essentially hardy and easy to keep, like the other members of the genus it benefits from soft and acidic water conditions and not-too-strong illumination.

The scissortail rasbora Rasbora trilineata is one of the most regularly seen rasboras and is a reliable, robust fish ideally suited to aquarium life. It is an attractive fish that has a greenish-silver body with a coppery tone, a black stripe running along the midline of the body, and yellow, black, and white markings on its tail. It has an endearing habit of twitching the two lobes of its brightly coloured tail-fin, from whence comes its common name. Scissortail rasboras get reach 10-13 cm in length, so need a fairly large tank with lots of swimming space.

One of the most beautiful rasboras is the red-line or glowlight rasbora Rasbora pauciperforata. A slender, medium-sized species, it gets to about 7 cm and sports a vivid coppery-red stripe running from the snout through the eye and onto the base of the tail. Otherwise the fish is essentially transparent. In aquaria this species has been found to be lively but a bit shy despite its size and is best kept in a roomy tank with small, gentle tankmates unlikely to startle it

Rising stars

Each year new rasboras appear in the trade, and many of these make excellent additions to the community tank. The yellow-tail rasbora Rasbora tornieri is a fairly large (up to 17 cm) species that lives close to the surface of the water, unlike most other rasboras which prefer a level lower down the water column. Wild fish feed primarily on insects that fall on the water’s surface, and certainly things like fruit flies and other small insects will be very much enjoyed by this species. As its name suggests, this fish has a yellow tail, but it also has a vivid yellow band running the length of the body and an attractive pearly-pink sheen to the body.

Another relative newcomer to the hobby is the fire rasbora Rasbora vaterifloris. A small (4 cm) fish with a beautiful deep-bodied, orange coloured body. Males have red fins, females yellow, and a group of these fish is a very attractive sight.

Two slender, rather small rasboras of the genus Boraras periodically turn up in the better aquarium stores, Boraras merah and Boraras urophthalmoides. The first of these, Boraras merah, is known as the phoenix rasbora and is a very vividly coloured creature with a reddish, semi-transparent body, a dark patch a short distance behind the gill covers, and various red blotches on the flanks, the base of the tail, and the dorsal fin. A few small black spots may also be seen elsewhere on the body. Reaching around 2 cm in length, this is a tiny fish ideally suited to a placid community aquarium with other miniature species such as sparkling gouramis and Corydoras hastatus. The sparrow or spice rasbora Boraras urophthalmoides is bigger, up to 4 cm, but has a similarly slender build. It bears an elongated black blotch on the flanks and red patches on the body and fins.

Two more small rasboras are the neon yellow rasbora Microrasbora kubotai and the zebra rasbora Microrasbora erythromicron. Neither of these exceeds a couple of centimetres in size. Microrasbora kubotai has a transparent, lemon-yellow body with a bold yellow band running along the midline of the fish. Microrasbora erythromicron are rather like miniature Barilius with a stocky but streamlined body with a distinct coppery hue and prominent vertical bands decorating the flanks. It also bears a small eyespot on the caudal peduncle.