The Red-Tailed Rasbora (Rasbora borapetensis) is a fish of the family Cyprinidae found in Asia in the Mekong, Chao Phraya, and Mae Klong basins, and also the northern Malay Peninsula. In the aquarium trade, it is known by a variety of other names, including Blackline Rasbora, Bora Bora Rasbora, and Brilliant Rasbora.
This species appears to be particularly hardy and adaptable and is found in polluted waters in some localities. It shows a preference for the shallow margins of gently flowing or still waters including ponds, ditches, reservoirs, and canals and is rather common across the majority of its range.
The Blackline Rasbora is a streamlined, silverfish with a dark brown or black, mid-lateral stripe reaching from the gill opening to the front of the caudal fin base. Above this line is a gold stripe. The caudal fin is bright red, and unlike Rasbora einthovenii, there is no black pigment. The two sexes look alike, but adult females are slightly larger than males. The fish grows to about 2.5 inches or 6 cm in length.
A tank measuring 60 cm x 37.5 cm x 30 cm / 70.8 litres is big enough to house a small group of these.
Choice of decor is not especially critical although the fish tend to show better colouration when maintained in a well-planted set-up with a dark substrate. The addition of some floating plants and driftwood roots or branches to diffuse the light entering the tank also seems to be appreciated and adds a more natural feel. Filtration does not need to be particularly strong as it mostly hails from sluggish waters and may struggle if there is a fast current in the.
Stomach analyses of wild specimens have revealed it to be a micro predator feeding on small insects, worms, crustaceans and other zooplankton. The aquarium will accept dried foods of a suitable size but should not be fed these exclusively. Daily meals of small live and frozen fare such as Daphnia, Artemia and suchlike will result in the best colouration and encourage the fish to come into breeding condition.
This species is very peaceful indeed making it an ideal resident of the well-furnished community tank. As it places no special demands in terms of water chemistry it can be combined with many of the most popular fish in the hobby including other small cyprinids as well as tetras, livebearers, rainbowfish, anabantoids, catfish and loaches. As always when selecting a compatible community of fish thorough research is essential and its small adult size must be a consideration. A community based around one of its native countries or river basins would also make an interesting project with possibilities from Thailand alone including various Badis, Betta, Trichogaster, Danio, Trigonostigma, Puntius, Crossocheilus, Pangio, Lepidocephalichthys and other species amongst others.
It’s a schooling species by nature and really should be kept in a group of at least 8-10 specimens. Maintaining it in decent numbers will not only make the fish less nervous but will result in a more effective, natural-looking display. Males will also display their best colours as they compete with one other for female attention.