Danio dangila

Danio: from Dhani, a Bengalese vernacular term for small, minnow-like cyprinids.

dangila: appears to be derived from a local vernacular name for the species.

Said to be found throughout the Ganges River basin although most records we've been able to find correspond to Nepal and the Brahmaputra drainage in India and Bangladesh.

The type specimens were apparently collected from the district of Munger, Bihar State, India through which the main Ganges channel flows, although all have since been lost.

It's also been reported from tributaries of the Brahmaputra in Bhutan, and, more recently, from Myanmar where it appears to be quite widely distributed as some collections occurred as far south as the state of Mon.

Based on images it seems the fish can vary considerably in patterning depending on locality. The fish from the East Khasi Hills district of Meghalaya State, north-east India, is now treated as a separate species, D. meghalayensis (see 'Notes').

The type series was collected from 'mountain streams' but the species has been collected from sluggish, swampy environments with dense marginal vegetation.

Given its extensive natural range it would seem this species is adaptable and able to colonise various habitat types at varying altitudes.

In the Barak River drainage, which flows through the north-east Indian states of Nagaland and Assam before bifurcating at the Bangladesh border, symaptric species include Barilius barna, B. bendelisis, B. dogarsinghi, Laubuca laubuca, Esomus danricus, Devario aequipinnatus, D. annandalei, D. devario, Rasbora daniconius, R. rasbora, Crossocheilus latius, Garra gotyla, G. lissorhynchus, G. nasuta, Balitora brucei, Acanthocobitis botia, Botia rostrata and Lepidocephalichthys guntea.

Very active and requires plenty of space to swim so a tank with dimensions of 120 ∗ 45 cm48 ∗ 18 in should be the minimum size considered to house a group.

Not difficult to keep in a well-maintained set-up though we recommend aquascaping the tank to resemble a flowing stream or river with a substrate of variably-sized, water-worn rocks, sand, fine gravel and perhaps some small boulders.

This can be further furnished with driftwood roots or branches, and while the majority of aquatic plants will fail to thrive in such surroundings hardy types such as Microsorum, Bolbitis or Anubias spp. can be grown attached to the décor should you wish.

Since it naturally occurs in pristine habitats it's intolerant to accumulation of organic pollutants and requires spotless water in order to thrive.

Though torrent-like conditions are unnecessary it also does best if there is a high proportion of dissolved oxygen and decent water movement so a good-sized external filter or powerhead(s) should be employed as necessary and weekly water changes of 30-50% aquarium volume considered routine.

Temperature: 16 – 24 °C61 – 75 °F

pH: Weakly acidic to neutral water within the range 6.5 – 7.5 is usually recommended.

Hardness: 2 – 15 dGH

Probably preys on insects and their larvae in nature. In the aquarium it's a largely unfussy feeder and will accept most foods.

A good quality dried product can be used as the staple diet but this should be supplemented with regular meals of small live and frozen fare such as chironomid larvae (bloodworm), Daphnia, Artemia, etc., for the best colouration and conditioning.

Not an aggressive fish but may upset very slow-moving or timid tankmates with its constant activity and vigorous feeding behaviour so can only be considered appropriate for larger tanks containing robust, similarly-sized fishes.

There are plenty of suitable choices including many cyprinids, loaches, cichlids, catfishes and characins although as always when selecting a compatible community of fish proper research is essential.

A community based around one of its native countries or river basins would also make a worthwhile project with some interesting alternatives (see 'Habitat').

It's a schooling species by nature and ideally should be kept in a group of at least 8-10 specimens.

Maintaining it in decent numbers will not only make the fish less prone to bouts of skittishness but will result in a more effective, natural looking display while any aggressive behaviour will normally be contained as the fish concentrate on maintaining their hierarchical position within the group.

Sexually mature females are usually rounder-bellied and exhibit a white stripe towards the distal edge of the anal-fin which is red in males.

The differences are especially clear when the fish are in spawning condition as the males intensify in colour and the females fill with eggs.

Like many cyprinids this species is an egg-scatterer that exhibits no parental care.

If the fish are in good condition they should spawn often, and in a densely-planted, mature aquarium it's possible that small numbers of fry may start to appear without intervention.

In general, however, it has proven trickier to breed than other danios, and the usual methods tend not to yield results.

We know of no report of this species spawning in aquaria. The spawning reported by US aquarist Dennis Ball was of the Meghalaya fish, now D. meghalayensis, and is described on that species' profile.

The vernacular name refers to the fact this species possesses exceptionally long barbels. Considering its apparent abundance in nature it remains uncommon in the hobby and little is written regarding its captive care.

The Meghalaya population was described as D. meghalayensis Sen & Dey 1985. Kottelat (2013) treated it as a synonym of D. dangila, but Kullander (2015) revalidated it as a separate species, with D. deyi as a probable synonym. It has a mainly striped, as opposed to spotted, pattern on the body, a smaller spot behind the gill cover, shorter barbels and more red in the fins than D. dangila.

In recent years it's become commonplace to refer to the stripes on the body and fins of danionins as follows:

- P stripe: or "pigment stripe" is the central, dark, lateral stripe on the body which extends into the caudal-fin in some species. Stripes above it are numbered P+1, P+2, etc. and those beneath P-1, P-2, P-3.
- A stripe: the central stripe on the anal-fin; the proximal stripe (above it) is A+1 and the distal stripe (beneath) A-1.
- D stripe: The submarginal dorsal-fin stripe.

Following Fang (2003) Danio spp. are characterised by the presence of an A stripe on the anal-fin and two or more P stripes on the caudal, plus some internal characteristics such as enlarged nasal lamellae.

The genus has undergone some significant taxonomic reshuffling in recent years following the publication of a series of phylogenetic studies.

Older, molecular, phylogenies tended to agree that it represented a monophyletic group consisting of two major clades; the 'Danio devario' group containing the larger, deeper-bodied species and the 'D. rerio' clade comprising the smaller, slimmer fish.

However in 2003 Fang conducted a more detailed study based on morphological characters which included members of other related genera, and the results suggested for the first time that the genus Danio as previously considered represents a polyphyletic grouping, i.e., not all members derived from a single common ancestor.

The genus name Devario was suggested for the larger species with Danio being applied only to the smaller fish (with the exception of the type species, D. dangila which can grow to around 89 mm3.5 in SL). Recent molecular studies by Mayden et al. (2007) and Fang et al. (2009) resulted in further changes, with the latter study considering the genus Danio to be composed of three subclades. These were subsequently split into distinct genera by Kottelat (2013), as follows:

The former species D. erythromicron, D. margaritatus, D. choprae and D. flagrans were grouped together in the revalidated genus Celestichthys Roberts, 2007. These exhibit unique body patterning consisting of vertical bars (D. erythromicron, D. choprae, D. flagrans) or light spots (D. margaritatus) and possess either very short barbels or none at all.

Kottelat (2013) left only the type species, D. dangila, in Danio, separated on the basis of its larger size and the shape of its caudal fin. Kullander (2015) then found that fish identified as D. dangila in Myanmar, India and Nepal include several species. He described D. assamila, D. catenatus, D. concatenatus and D. sysphigmatus and recognised D. meghalayensis as valid. With D. annulosus (Kullander et al. 2015) they make up the chain danios. All of them have more branched dorsal-fin rays than other danios, a long first ray in the pelvic and pectoral fins, a pattern of dark rings along the flanks, very long barbels and a broad caudal fin in adults.

The remaining species, of which D. rerio is thought to be the most ancient, were placed in the revalidated genus Brachydanio Weber & de Beaufort, 1916. Kullander (2015) did not follow this split, because phylogenetic analyses strongly support a single Danio in the sense of Fang (2003), with Devario a separate genus. The Catalog of Fishes and FishBase both keep all of these species in Danio.