With seemingly boundless energy and perpetual inquisitiveness, danios have been great favorites with tropical fishkeepers from the early days of the modern hobby. The zebra danio (Brachydanio rerio) is too well-known to even need description. As one of the most prolific egg-laying tropical fish it has been available in large numbers at bargain prices since its introduction into the hobby at the beginning of the century.
Native to India, zebra danio stocks are occasionally shipped from there to the world's aquarium markets. But most supplies are commercially bred in Hong Kong, Singapore, Florida and other established fish breeding centers. Although small and normally peaceful, some zebra danios are capable of being quite aggressive.
Long-finned varieties and golden forms of zebra danios enhance the attraction of the species to many fishkeepers. Long-finned varieties of pearl (B. albolineatus) and leopard (B. frankei) danios are also freely available now.
One species that used to be readily available (at least to the British markets) up to some 20 years ago was the daintily marked spotted danio (B. nigrofasciatus). However, it is now something of a rarity to the hobby. Why this pretty little danio disappeared from commercial breeding programs is not known, but it might be that it was ousted by the leopard danio when it made its debut in the hobby.
The origins of the leopard danio are uncertain. There is no such fish in the wild. It just "appeared" in the hobby in 1963 and is thought to have resu1ted from crossing other Brachydanio species, probably in Eastern Europe. A first-generation cross between zebra and pearl danios may give a clue to the actual origins of the leopard danio. However the strain originated, it has become a firm favorite with hobbyists across the world.
Color variations are producing some very eye-catching danio varieties. The golden zebra is questionably an "improvement" on the original wild fish. The golden cast masks the stark contrast between the steel-blue body horizontally embellished with silver or brassy stripes.
A colorful variety of the pearl danio has been dubbed the rainbow danio. This variety has lost the distinct lateral stripe of the regular form, and retains only a shadow of that feature. The shining pearly body has metallic blue and red areas.
A blue danio has resulted from "sports" of leopard danio breeding. The spotted markings have diminished appreciably, leaving a silvery blue coloring in prominence.
One of the "close cousins" of the little Brachydanio species is the dadio (Chela dadyburjori). This pretty little fish looks very much like a danio, and certainly comes from the same huge family of Cyprinidae. But its sub-family is Cultrinae, unlike the Brachydanio species, which are of the sub-family Rasborinae.
For the hobbyist, however, such scientific quibbles are not important, and this stylish little fish might well have been given a common name of "something" danio. The body shape is a little deeper and the finnage more elongate than that of the Brachydanio. The dadio is also somewhat less robust, although once acclimated to its surroundings it will flourish without special attention.
Another close cousin comes in the elegant form of the blue hatchetfish (Chela caeruleostigmata). A bit more scientific gobbledygook is in order. This species was once named Laubuca laubuca, which would put it in the sub-family Abraminae, but it is now correctly placed in the genus Chela, sub-family Cultrinae. Growing to about 2 1/3 inches, this species begins to dwarf the previously discussed Brachydanios and the dadio. But in every other way, it is perfectly compatible with its cousins, and is equally undemanding.
The blue hatchetfish has a deeply keeled body, which accounts for its common name. As the fish swims and its body moves, reflecting light at different angles, the metallic colors shine with beautiful variation. This species is not readily available, but it is highly sought after.
The giant danio (Danio aequipinnatus) has become something of a mystery fish through domestic breeding. The wild form has a broken patchwork of yellow markings on the lower part of its flanks and immediately behind the gills. It might also have reddish anal and tail fins.
The giant danio originally came in as imports from Sri Lanka and occasionally India, where it occurs in western coastal regions. Farm-bred stocks are now frequently received into the hobby market, and it is thought that some hybridizations with the queen danio (Danio regina) has taken place to produce two rather similar looking fish. Farm-bred fish might have some blood from either strain in their stock, as they frequently do not match up to either wild form, but seem to combine features from both.
There is often understandable confusion between the giant danio and the queen danio. The queen danio has strong, clean lines of gold running the length of its body, and far richer coloring. The flanks on either side of these stripes may be anything from emerald green to steel blue.
The queen danio originates in Southeast Asia and can grow to about 4 to 4 1/3 inches. It is truly a giant among the other tiny members of the sub-family Rasborinae.
The Bengal danio (Danio devario) is often mistaken for the previous species. The female has a markedly deeper body than the giant danio, but the male has a similar profile. Potential growth is to the same length as the giant danio. It is a very peaceful species and eminently suitable to join a danio community without problems.
Metallic blues, greens and golds are the predominant colors associated with the danios and their cousins, making a handsome contrast to their more gaudily colored companions in the peaceful community aquarium. Constant busy movement is a common feature, as is a propensity to move in a schooling formation.
Brachydanio species will usually occupy the upper levels of the aquarium, while the other community species tend to be mid-water swimmers. They take a wide variety of foods. Danios generally prove easy to breed, with no special fuss or preferences. The danios are an ideal beginner's fish, adding dash and delight to the aquarium.