Danio sp. 'TW01'

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

Apparently discovered close to the coastal town of Gwa in Rakhine State, western Myanmar.

Rakhine is largely cut off from the rest of the country by the Rakhine Yoma/Arakan mountains which form a natural barrier along its eastern side.

Myanmar can be considered a centre of diversity for the genus with over ten species, the majority of which are endemic to the country.

Rakhine is located within a tropical monsoon region and has a pronounced rainy season between May and October, while at other times it can be quite dry.

The streams thus swell in depth by a metre or more and flow much more rapidly during the wet season.

An aquarium with base dimensions of 120 ∗ 30 cm48 ∗ 12 in or equivalent should be the smallest considered.

Looks particularly effective in a heavily-planted arrangement with a darker substrate, and may appear paler in sparsely-decorated set-ups.

We suggest maintaining it in a well-planted aquarium or set-up designed to resemble a flowing river or stream, with a substrate of variably-sized rocks and gravel and some large water-worn boulders.

Additional powerhead(s) or filter outlets can be used to provide flow but torrent-like conditions should be avoided since small danionins tend to occupy calmer stretches and marginal zones in nature.

Driftwood roots, branches and aquatic plants, with hardy genera such as Microsorum, Bolbitis or Anubias ideal since they can be grown attached to the décor, can also be added.

The aquarium must have a very tightly-fitting cover as members of this genus are accomplished jumpers and can fit through surprisingly small gaps.

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

A good quality dried product or two can be used as the staple diet but this should be supplemented with regular meals of small live and frozen fare such as bloodworm, Daphnia, Artemia, etc. for the fish to show 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.

Other species from the Rakhine Yoma available in the trade include Rasbora daniconius, R. rasbora, Garra flavatra, G. spilota, Lepidocephalichthys berdmorei, Opsarius barna and Devario xyrops.

Though gregarious by nature it's a shoaling rather than schooling fish which only groups together very tightly when threatened, while at other times rival males spar regularly.

Maintaining it in numbers of 10 or more will allow sub-dominant fish of both sexes some respite from the alpha individual(s) which can be quite aggressive at times.

The latter are clearly distinguishable by their brighter, more intense colouration.

Mature males are more colourful and noticeably slimmer plus they have orange distal edges to the ventral and anal fins, these being white in females.

In groups containing multiple males one or more specimens typically develops 'alpha' status and displays more intense colouration.

Like most cyprinids this species is an egg-scattering spawner that exhibits no parental care.

That is to say when the fish are in good condition they will spawn often and in a densely-planted, mature aquarium it is possible that small numbers of fry may start to appear without human intervention.

However if you want to increase the yield of fry a slightly more controlled approach is required and we suggest upscaling an approach that has proven successful for smaller members of the genus.

The adult group can still be conditioned together but one or more long, shallow, say 65-85 litre, containers should also be set up and half-filled with water.

Much of the available space should be filled with a suitable spawning medium such as Java moss, wool mops or a spawning grid.

The water should be of slightly acidic to neutral pH with a temperature towards the upper end of the range suggested above.

An internal power filter can be added initially and this should be positioned so that the flow is directed down the full length of the tank.

When the adult fish are well-conditioned and the females appear full of eggs one or two pairs should then be introduced to each container.

Spawning can be initiated by adding small amounts of cool water every few hours in such a way that the tank is gradually topped up and feeding small amounts of live and frozen foods, or by performing a large (50-60%) water change in the evening.

Several spawning events will probably occur before a female is spent of eggs.

The adults will eat any they find and are best removed once eggs are spotted.

At this point the power filter (if using) should be switched for a mature sponge-type unit in order to avoid fry being sucked into the mechanism.

Incubation in is temperature-dependant to an extent but usually takes between 3-7 days with the young free-swimming 24 to 48 hours later.

Initial food should be Artemia nauplii or a proprietary dry food of sufficiently small grade.

It remains unclear whether this represents an undescribed species or geographical form of D. feegradei since it lacks pale spots on the body but is otherwise comparable.

The easiest way to distinguish it from the superficially similar species 'Inlecypris' maetaengensis and 'I.' shanensis is by the characteristic dark marking on the caudal peduncle which is missing in the other two.

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 the caudal-fin, which in adults is only slightly emarginate or even truncate in shape, a feature it shares only with Tinca tinca (the common tench) among other cyprinids.

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.