The identity of this species was unclear for a number of decades prior to its redescription by Ng and Kottelat (2013)[10].
The confusion originated with Brittan (1954) who misidentified specimens of R. tornieri as R. dusonensis and was exacerbated by Alfred (1963) who concluded that the holotype of R. dusonensis was conspecific with R. myersi.
Kottelat (1991) subsequently considered R. myersi, a plain grey-coloured species, to be a synonym of R. dusonensis but this conclusion was incorrect and both species are currently considered valid (Ng and Kottelat, 2013)[10].
R. dusonensis is very similar to R. tornieri and these two can be distinguished from other members of the genus by the following combination of characters: a broad, dark brown, sharply-defined midlateral body stripe extending from the opercle to the caudal-fin base; a dark brown supralateral stripe and dorsum separated from the midlateral stripe by a light longitudinal area; 12–14 predorsal scales; dorsohypural distance equal to or slightly less than the distance between the dorsal-fin origin and posterior orbital margin; 14 circumpeduncular scales; caudal-fin brightly coloured in life.
R. dusonensis differs from R. tornieri in possessing a bright yellow (vs. carmine red in R. tornieri) caudal-fin with a broad, dark distal margin (vs. with or without a narrow dark margin), and a more slender caudal peduncle fitting 8.5–9.6 times in SL and measuring 10.4–11.7 % SL (vs. 7.9–8.8 times and 11.4–12.6 % SL, respectively).
Both R. dusonensis and R. tornieri are included in the R. argyrotaenia species group (sensu Brittan, 1954, see below) of which members share the following characters: 14 circumpeduncular scale rows, the dorsohypural distance equal to or slightly less than the distance between the dorsal-fin origin and posterior orbital margin, 1 or 1½ scale rows between the lateral line and the origin of the pelvic-fin, and a continuous dark midlateral stripe from the opercle to the base of the caudal-fin.
Within the R. argyrotaenia group the only other species possessing a bright yellow caudal-fin is R. aurotaenia but R. dusonensis can be distinguished from it by possessing a subpeduncular stripe (vs. lacking in R. aurotaenia), sharply-contrasted midlateral and supralateral stripes with discrete edges and the light area between them almost completely lacking pigment (vs. stripes with indistinct edges and the light area partially-pigmented), and a more slender body with depth fitting 4.0–4.8 times in SL (vs. 3.7–4.0).
The identity of R. argyrotaenia itself is uncertain with the type series consisting of fish from several localities and possibly comprising multiple taxa.
As currently recognised it occurs in Java (the type locality), Sumatra, Borneo and the Malay Peninsula but this distribution represents an assemblage which will eventually be split into several species (Kottelat, 2012)[9].
Rasbora is among the more speciose genera in the family Cyprinidae with members distributed throughout much of Southeast Asia.
The last major review of the genus was published by Brittan (1954) in which the species were arranged into eight groups (referred to as 'species complexes' by the author) and it has long been recognised as a 'catch-all' polyphyletic grouping because no synapomorphy has been proposed to diagnose it.
Brittan diagnosed the genus by the following combination of characters: presence of a symphyseal knob on the lower jaw; three pharyngeal tooth rows; one or two scales between the lateral-line scale row and pelvic-fin insertion; dorsal-fin insertion opposite to pelvic-fin insertion or slightly behind it; seven branched dorsal-fin rays and five branched anal-fin rays; absence of barbels.
A number of former members of Rasbora sensu Brittan have been placed in new genera by various authors, these including Rasboroides, Boraras, Trigonostigma and Sundadanio.
More recently Liao et al. (2010) conducted a morphological phylogenetic analysis of Rasbora and related genera with six clades (A-F) recognised in their results.
They erected four new genera, all containing former members of Rasbora, in order to preserve monophyly of Boraras, Horadandia, Rasbora, Rasboroides and Trigonostigma.
Clades A and B were monotypic with the species formerly known as R. brittani reclassified as Kottelatia brittani and R. dorsiocellata as Brevibora dorsiocellata, respectively (Brevibora currently contains two species).
Clade C comprised the genera Boraras, Horadandia, Rasboroides and Trigonostigma plus three species previously included in Rasbora which were moved into the new genera Trigonopoma (containing T. gracile and T. pauciperforatum) and Rasbosoma (containing R. spilocerca).
The results for Boraras and Trigonostigma were found to be inconclusive in some respects and further work regarding their phylogenetic position was recommended.
Clade D included Rasbora semilineata, R. borapetensis, R. rubrodorsalis and an undescribed fish similar to R. beauforti while clade E consisted of R. daniconius, R. hubbsi, R. paucisqualis, R. wilpita, R. kobonensis, R. ornata and R. cf. daniconius.
Clade F was subdivided into two groupings, the first containing R. einthovenii, R. elegans and R. cephalotaenia and the second R. lateristriata, R. argyrotaenia, R. volzii, R. paviana, R. rasbora (plus an undescribed, similar fish), R. caudimaculata and R. trilineata.
As this final clade contains the type species (see below) its members retained the generic name Rasbora as did those included in clade E because they weren't considered to differ sufficiently to warrant the erection of a new grouping.
Many Rasbora species weren't included in the study however so the authors proposed an arrangement comprising six species groups, namely the R. semilineata, R. trifasciata, R. daniconius, R. einthovenii, R. argyrotaenia and R. sumatrana groups, plus a number of species which were not included in any group.
Shortly afterwards a paper investigating systematics of the subfamily Danioninae was published by Tang et al. (2010) and their conclusions differed significantly, however.
The four new genera proposed by Liao et al. were synonymised with Rasbora as were Boraras and Trigonostigma since their phylogenetic placement would otherwise have rendered Rasbora polyphyletic and require that it be broken up into many different genera.
Although such actions may turn out to be justified, with the monophyly of Boraras and Trigonostigma strongly supported, a revision of the entire genus Rasbora would be required which was beyond the scope of the authors' study.
This more conservative approach to the group's taxonomy was therefore adopted although this will probably be subject to considerable change as additional studies are published.
Here on SF we've chosen to retain the system proposed by Liao et al. (2010) for the time being since generic names such as Boraras and Trigonostigma are well-established in aquarium literature and appear likely to be revalidated in the future.
The identity of the type species, often given as R. rasbora in the past, is no longer in question.
When Bleeker first referred to the name Rasbora in 1859 only four nominal members were included of which R. cephalotaenia (known as Leuciscus cephalotaenia at the time) should be considered the type.
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