|Cyprinus (Danio) dangila
Brachydanio Weber & de Beaufort, 1916
The name "danio" comes from the Bangla name dhani, meaning "of the rice field". Danio was described in the early 19th century by Francis Hamilton, a surgeon working for the British East India Company. Two of the species included by him in the genus, still remain valid — Danio rerio and Danio dangila. About a century later (1916) and with many more spcies described in the meantime, the genus was split; the larger species into Danio and the smaller species, such as D. rerio, into the new Brachydanio. In 1991, though, the two genera were recombined; most larger species formerly within the Danio genus, such as the giant danio, have now been reclassified into the Devario genus. Also, Brachydanio is now a junior synonym of Danio.
There are currently 25 species recognized in this genus:
- Danio absconditus S. O. Kullander & Britz, 2015 (Black barred danio) 
- Danio aesculapii S. O. Kullander & F. Fang, 2009 (Panther danio)
- Danio albolineatus (Blyth, 1860) (Pearl danio)
- Danio annulosus S. O. Kullander, Rahman, Norén & Mollah, 2015 
- Danio assamila S. O. Kullander, 2015 
- Danio catenatus S. O. Kullander, 2015 
- Danio choprae Hora, 1928 (Glowlight danio)
- Danio concatenatus S. O. Kullander, 2015 
- Danio dangila (F. Hamilton, 1822) (Moustached danio)
- Danio erythromicron (Annandale, 1918) (Emerald dwarf rasbora)
- Danio feegradei Hora, 1937 (Yoma danio) 
- Danio flagrans S. O. Kullander, 2012 
- Danio jaintianensis (N. Sen, 2007)
- Danio kerri H. M. Smith, 1931 (Blue danio)
- Danio kyathit F. Fang, 1998
- Danio margaritatus (T. R. Roberts, 2007) (Galaxy rasbora)
- Danio meghalayensis N. Sen & Dey, 1985 (Meghalaya danio)
- Danio nigrofasciatus (F. Day, 1870) (Spotted danio)
- Danio pulcher H. M. Smith, 1931 (Blue-redstripe danio) 
- Danio quagga S. O. Kullander, T. Y. Liao & F. Fang, 2009
- Danio rerio (F. Hamilton, 1822) (Zebrafish)
- Danio roseus F. Fang & Kottelat, 2000 (Rose danio)
- Danio sysphigmatus S. O. Kullander, 2015 
- Danio tinwini S. O. Kullander & F. Fang, 2009 (Gold-ring danio)
- Danio tweediei Brittan, 1956 (Kedah danio) 
Some undescribed species or varieties, which may be represented by recently described species above, include:
Danios are native to the fresh water rivers and streams of South and Southeast Asia. Many species are brightly colored, and are available as aquarium fish worldwide. A number of the species, only recently discovered in remote inland areas of Myanmar, do not yet have scientific names.
Most species of Danio have two pairs of long barbels, and they are generally characterised by a pattern of horizontal stripes, rows of spots, or vertical bars. Sizes range from about 25 to about 90 mm (1–3.4 in) in length. The smaller species generally do not live for more than two to three years, and are probably annual fish in the wild.
In the aquarium
The care of members of the genus Danio is rather similar and easily generalized. They are easy to keep.
All of these fish are primarily surface feeders. They are omnivorous in the aquarium and will accept a wide variety of foods, though flake food is appropriate. Living in aquaria, live/frozen flaked foods are suitable, especially brine shrimp and sinking tablets. Danios are voracious eaters; timid feeders may starve in community tanks with danios. When conditioning danios for breeding, it is advisable to feed them plenty of fresh foods.
Although boisterous and liable to chase each other and other fish, they are good community fish and will not generally attack each other or other fish, although they occasionally nip fins, more by accident than design; like most fish, they will eat eggs and any fish small enough to fit into their mouths.
They are best kept in a tank long enough for their active swimming, preferably with a current from a power filter (or at least airstone) as they often live in fast-flowing streams in the wild. Generally, this also results in them being subtropical with cooler temperatures. They are good jumpers, so a tight-fitting lid is recommended.
As a schooling fish, they prefer to be in groups of six or more. Danios prefer water with a pH between 6.0 and 8.0, hardness no more than 19.0 dGH, a carbon hardness of 8 to 12 KH, and a temperature range of 20–26 °C (68–80 °F); the lower end of the temperature range is ideal.
Some species of Danio, such as the zebra danio, are among the easiest aquarium fish to breed. Other species, such as Danio kyathit, are far harder to spawn. All scatter their eggs over the substrate. The eggs are not adhesive, and hatch within two or three days. Eggs will be eaten enthusiastically unless protected by a layer of marbles or heavy substrate planting.
Hybrids between some Danio species have been bred; the young can be raised to maturity, but are sterile.
- Danionins - full details of all fish related to Danio, including those species known as danios which are no longer scientifically classified in Danio
- Devarios - details of the species within the genus Devario
- Spence, R., Gerlach, G., Lawrence, C. & Smith, C. (2007). "The behaviour and ecology of the zebrafish, Danio rerio" (PDF). Biological Reviews for the Cambridge Philosophical Society, 83 (1): 13–34.
- Fang, F. (2003). "Phylogenetic Analysis of the Asian Cyprinid Genus Danio (Teleostei, Cyprinidae)". Copeia, 2003 (4): 714–728.
- Kullander, S.O. & Britz, R. (2015). "Description of Danio absconditus, new species, and redescription of Danio feegradei (Teleostei: Cyprinidae), from the Rakhine Yoma hotspot in south-western Myanmar" (PDF). Zootaxa, 3948 (2): 233–247.
- Kullander, S.O., Rahman, M.M., Norén, M. & Mollah, A.R. (2015). "Danio annulosus, a new species of chain Danio from the Shuvolong Falls in Bangladesh (Teleostei: Cyprinidae: Danioninae)" (PDF). Zootaxa, 3994 (1): 53–68.
- Kullander, S.O. (2015). "Taxonomy of chain Danio, an Indo-Myanmar species assemblage, with descriptions of four new species (Teleostei: Cyprinidae)" (PDF). Ichthyological Exploration of Freshwaters, 25 (4): 357–380.
- Kullander, S.O. (2012): Description of Danio flagrans, and redescription of D. choprae, two closely related species from the Ayeyarwaddy River drainage in northern Myanmar (Teleostei: Cyprinidae). Ichthyological Exploration of Freshwaters, 23 (3): 245-262.
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