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Rasbora dorsinotata KOTTELAT, 1987

Classification

Order: Cypriniformes Family: Cyprinidae

Distribution

Type locality is ‘Mae Nam Huey Bon, kilometer 45 on road from Amphoe ThaWang Pha to Amphoe Chiang Kham, Chiang Rai Province, Thailand’, and this species appears restricted to the Mekong and upper Chao Phraya river basins in northern Thailand and northern Laos.

The specimens pictured here were collected from the upper Wang River, a tributary of the Chao Phraya in Thailand , and it’s also known from Nam Ma Oun, Louang  Nam Tha (Luang Namtha) province, Laos.

Habitat

Displays a preference for smaller tributaries containing clear, flowing water rather than main river channels, and is apparently abundant in such habitats.

Maximum Standard Length

The largest specimen known measured 43 mm.

Aquarium SizeTop ↑

An aquarium with base dimensions of 90 ∗ 30 cm or equivalent should be the smallest considered.

Maintenance

Should not prove 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 MicrosorumBolbitis or Anubias spp. can be grown attached to the décor.

Since it naturally occurs in pristine habitats it’s likely to prove intolerant to accumulation of organic pollutants and require spotless, well-oxygenated water in order to thrive.

A degree of water movement should also be appreciated, and weekly water changes of 30-50% tank volume should be considered routine.

Water Conditions

Temperature20 – 25 °C

pH6.0 – 7.5

Hardness36 – 215 ppm

Diet

Probably feeds mostly on both aquatic and terrestrial invertebrates as with similar members of the genus.

In the aquarium it should accept dried foods of a suitable size but daily meals of small live and frozen fare such as Daphnia, bloodworm and suchlike will result in the best colouration and encourage the fish to come into breeding condition.

Behaviour and CompatibilityTop ↑

Likely to be peaceful and an ideal resident of the larger, well-furnished community tank.

A community based around fish from the Chao Phraya river would also make an interesting project with suitable species available in the hobby including Acantopsis choirorhynchos, Yasuhikotakia sidthimunki, Danio albolineatus, Opsarius pulchellus, Mystacoleucus marginatus, Garra cambodgiensis plus various Homaloptera, Lepidocephalichthys, Schistura and Crossocheilus spp.

Rasboras are gregarious  fishes and should be maintained in groups of at least six individuals to get the best out of them. They will show better colours, are more confident and display more natural behaviour.

Sexual Dimorphism

Mature females should be noticeably rounder-bellied and probably grow a little larger than males.

Reproduction

Possibly unrecorded, but recommendations for closely-related species are as follows:

Like most small cyprinids Rasbora spp. are egg-scattering free spawners exhibiting no parental care. When in good condition they will spawn often and in a mature aquarium it’s possible that small numbers of fry may start to appear without intervention.

However if you want to maximise yield a more controlled approach is required. The adult group can still be conditioned together but a separate aquarium or container(s) should also be set up and filled with mature water.

This should be very dimly lit and the base covered with some kind of mesh of a large enough grade so that the eggs can fall through but small enough so that the adults cannot reach them.

The widely available plastic ‘grass’-type matting can also be used and works well, as does a layer of glass marbles. Alternatively filling much of the tank with a fine-leaved plant such as Taxiphyllum spp. or spawning mops can also return decent results.

An air-powered sponge filter or air stone(s) should also be included to provide oxygenation and water movement, or small internal power filter installed and positioned in such a way that the flow is directed down the length of the tank.

One or two pairs of conditioned adults should then be introduced to each container. Spawning can often be intiated by adding small amounts of cool water every few hours and feeding small amounts of live and frozen foods. Several spawning events will probably occur before a female is spent of eggs.

The adults will likely eat any eggs they find and are best removed after a couple of days at which point the power filter should be switched for a mature sponge-type unit in order to avoid fry being sucked into the mechanism.

Incubation in Rasbora eggs is temperature-dependant to an extent but usually takes between 18 and 48 hours with the young free-swimming 24 to 48 hours later. Initial food should be Artemia nauplii, microworm, vinegar eels, etc.

NotesTop ↑

R. dorsinotata is poorly-documented in the aquarium literature and we’re unsure if it’s been exported for the hobby.

It can be told apart from similar-looking species by the following characters: dorsal-fin with a black tip; a black lateral stripe extending from the opercle to posterior half of caudal peduncle, ending in a rounded spot which does not extend onto the caudal-fin; lateral stripe wider anterior to dorsal-fin origin; 26+1-2 lateral line scales; 4½ scales between lateral line and dorsal-fin origin.

Rainboth’s ‘Fishes of the Cambodian Mekong’ characterised members of Rasbora by: possession of an unbranched, non-spiny first dorsal-fin ray; seven soft dorsal rays; origin of the dorsal-fin in the middle of the body; five branched anal-fin rays; a small mouth not extending below the eye; absence of barbels.

It’s long been recognised as a polyphyletic lineage as noted by Kottelat (1999) among others, and in 2010 the results of a phylogenetic analysis by Liao et al. suggested a number of changes in order to improve the taxonomy.

The authors found species of rasborin genera to represent a monophyletic grouping existing in six clades and erected four new genera containing former members of Rasbora in order to preserve monophyly of the existing groups.

The first two of these clades contain new groupings Kottelatia and Brevibora, respectively. The third comprises BorarasHoradandiaRasboroides, and Trigonostigma, plus new genera Trigonopoma and Rasbosoma.

However the results for Boraras and Trigonostigma were found to be inconclusive in some respects and further work regarding their phylogenetic position was recommended.

The fourth clade includes Rasbora semilineataR. borapetensisR. rubrodorsalis, and an undescribed fish similar to R. beaufortiClade five consists of R. daniconiusR. hubbsiR. paucisqualisR. wilpita (plus allies), R. kobonensisR. ornata, and R. cf. daniconius.

Clade six is subdivided into two groupings. The first contains R. einthoveniiR. elegans, and R. cephalotaenia, and the second R. lateristriataR. argyrotaeniaR. volziiR. pavianaR. rasbora (plus an undescribed related fish), R. caudimaculata, and R. trilineata.

As this final clade contains R. cephalotaenia, the type species of Rasbora, its members retain the generic name as do members of clade five because they don’t differ sufficiently to warrant erection of a new genus or genera.

Unfortunately many species weren’t included in the analysis leading to confusion regarding the correct placement of the 40 or so other Rasbora species, in particular.

As the genus had previously been split into various ‘species groups’ (groups of closely-related taxa) dating back to Brittan (1972, who referred to them as ‘species complexes’) Liao et al. proposed the following arrangement whilst noting it may be subject to change in the future:

R. semilineata species group: R. semilineataR. borapetensisR. rubrodorsalis.
R. trifasciata species group: R. trifasciataR. amplistrigaR. bankanensisR. diesR. ennealepisR. hubbsiR. johannaeR. meinkeniR. paucisqualisR. rutteniR. sarawakensisR. taytayensisR. tobanaR. tuberculata.
R. daniconius species group: R. daniconiusR. caveriiR. kobonensisR. labiosaR. ornataR. wilpita.
R. einthovenii species group: R. einthoveniiR. cephalotaeniaR. elegansR. jacobsoniR. kalochromaR. kottelatiR. nematotaeniaR. tubbi.
R. argyrotaenia species group: R. argyrotaeniaR. aprotaeniaR. aurotaeniaR. baliensisR. borneensisR. bunguranensisR. dusonensisR. everetiR. hobelmaniR. hossiR. lateristriataR. laticlaviaR. leptosomaR. philippinaR. septentrionalisR. spilotaeniaR. steineriR. tawarensisR. tornieriR. volzii.
R. sumatrana species group: R. sumatranaR. atridorsalisR. calliuraR. caudimaculataR. dorsinotataR. noturaR. pavianaR. rasboraR. subtilisR. trilineataR. vulgaris.

Not classified: R. beaufortiR. chrysotaeniaR. gerlachi (validity in question), R. kalbarensisR. reticulataR. vulcanus (possibly members of a different, unnamed, genus) and R. zanzibarensis (identity in question).

Shortly afterwards a paper investigating systematics of the subfamily Danioninae was published (Tang et al. 2010).

The results differed significantly and the four new genera of Liao et al., plus Boraras and Trigonostigma, were synonymised with Rasbora based on an incomplete knowledge of relationships within the group, an approach described as ‘more conservative’.

Though neither conclusion can be deemed 100%  the system of Liao et al. is followed here on SF pending future studies, if only because we prefer to retain the familiar generic names Boraras and Trigonostigma. In addition, species described post-2010 are not included in the list above.

References

  1. Kottelat, M., 2001 - WHT Publications, Colombo: 1-198
    Fishes of Laos.
  2. Kottelat, M., 2000 - Journal of South Asian Natural History 5(1): 83-90
    Notes on taxonomy, nomenclature and distribution of some fishes of Laos.
  3. Kottelat, M., 1999 - Raffles Bulletin of Zoology 47(2): 591-600
    Nomenclature of the genera Barbodes, Cyclocheilichthys, Rasbora and Chonerhinos (Teleostei: Cyprinidae and Tetraodontidae), with comments on the definition of the first reviser.
  4. Liao, T. Y., Kullander, S. O. and F. Fang, 2010 - Zoologica Scripta 39(2): 155-176
    Phylogenetic analysis of the genus Rasbora (Teleostei: Cyprinidae).
  5. Mayden, R. L., K. L. Tang, K. W. Conway, J. Freyhof, S. Chamberlain, M. Haskins, L. Schneider, M. Sudkamp, R. M. Wood, M. Agnew, A. Bufalino, Z. Sulaiman, M. Miya, K. Saitoh, and S. He, 2007 - Journal of Experimental Zoology, Molecular Development and Evolution 308B: 1–13
    Phylogenetic relationships of Danio within the order Cypriniformes: a framework for comparative and evolutionary studies of a model species.
  6. Tang, K. L., M. K. Agnew, W. J. Chen., M. V. Hirt, T. Sado, L. M. Schneider, J. Freyhof, Z. Sulaiman, E. Swartz, C. Vidthayanon, M. Miya, K. Saitoh, A. M. Simons, R. M. Wood and R. L. Mayden, 2010 - Molecular Phylogenetics and Evolution 57(1): 189-214
    Systematics of the subfamily Danioninae (Teleostei: Cypriniformes: Cyprinidae).

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