Rasbora dorsinotata

Cyprinidae

The specimens in our images originated from the upper Wang River in northern Thailand, a tributary of the Chao Phraya system, and the species has also been recorded from Laos. To date we have been unable to obtain any additional or more specific locality details.

Little information is available but presumably it is a pelagic species inhabiting streams, tributaries and rivers.

Expect it to reach around 4"/10cm.

An active species and a group will need a tank measuring at least 48" x 18" x 18"/120cm x 45cm x 45cm/255 litres.

Choice of decor is not as critical as water quality and the amount of open swimming-space provided. We suggest keeping it in a large, well-planted aquarium or alternatively it would look superb in a set-up designed to resemble a flowing river with a substrate of variably-sized rocks and gravel and some large water-worn boulders. A rivertank manifold could also be constructed to provide naturalistic unidirectional flow. The tank can be further furnished with driftwood branches and aquatic plants for aesthetic value. While the vast majority of the latter will fail to thrive in such conditions hardy species such as Java fern, Bolbitis or Anubias can be grown attached to the decor.

In either situation the tank must have a very tightly-fitting cover as rasboras are accomplished jumpers and can escape through the tiniest of gaps. Like other members of the genus it is likely to be intolerant to the accumulation of organic wastes and requires spotless water at all times in order to thrive.

68 - 77°F/20 – 25°C

6.0 - 7.5

2 - 12°H

Probably feeds mostly on invertebrates both aquatic and terrestrial in nature as with similar members of the genus. In the aquarium it should accept dried foods of a suitable size but should not be fed these exclusively. 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.

This species is likely to be very peaceful indeed and an ideal resident of the larger, well-furnished community tank. As it should place no special demands in terms of water chemistry it may be combined with many of the most popular fish in the hobby including other cyprinids as well as tetras, livebearers, rainbowfish, anabantoids, catfish and loaches. 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 members of Homaloptera, Lepidocephalichthys, Schistura and Crossocheilus.

Rasboras are gregarious species by nature and really should be kept in a group of at least six to get the best out of them in the aquarium. The fish show better colours in the presence of conspecifics, are less nervous and the display on the whole is far more natural-looking.

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

We're not sure if this species has been bred in the hobby although it should certainly be possible. Like most cyprinids it is an egg-scattering, continuous 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 48" x 12" x 12"/120cm x 30cm x 30cm/113 litre containers should also be set up and half-filled with water. These 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 it but small enough so that the adults cannot reach them. The widely available plastic 'grass'-type matting can also be used and works very well for other species. The water itself 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. Try to initiate spawning 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. 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 and/or microworm.

Rasbora dorsinotata is poorly-documented in the aquarium literature and we're not even sure if it has been exported for the hobby. It appears to be most easily-distinguished from similar species such as R. sumatrana, R. paviana , etc. by the presence of a dark blotch in the dorsal fin and may be worth looking out for among shipments of wild fish from northern Thailand and Laos.

Rainboth's 'Fishes of the Cambodian Mekong' characterised members of Rasbora by possession of an unbranched, non-spiny first dorsal fin ray and 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 and a lack of barbels. It's long been recognised as a polyphyletic lineage as noted by Kottelat (1999) amongst others, and in 2009 the results of a phylogenetic analysis by T. Y. Liao et al. suggested a number of changes in order to improve the taxonomy. The authors found species of rasborin genera to actually represent a monophyletic grouping existing in six clades and erected four new genera (all containing former members of Rasbora) in order to preserve monophyly of the existing groups i.e. Boraras, Horadandia, Rasbora, Rasboroides and Trigonostigma.

According to the authors the first two clades are monotypic; R. brittani should now be referred to as Kottelatia brittani  and R. dorsiocellata as Brevibora dorsiocellata . The third clade comprises Boraras brigittae , Horadandia atukorali , Rasboroides vaterifloris , Trigonostigma heteromorpha  and three species previously included in Rasbora but also moved into new genera; Trigonopoma gracile , T. pauciperforatum  and Rasbosoma spilocerca . The results for B. brigittae  and T. heteromorpha  were found to be inconclusive in some respects and further work regarding their phylogenetic position was recommended.

The fourth clade includes Rasbora semilineata, R. borapetensis , R. rubrodorsalis  and an undescribed fish similar to R. beauforti. Clade five consists of R. daniconius, R. hubbsi, R. paucisqualis, R. wilpita , R. kobonensis, R. ornata and R. cf. daniconius. Clade six, meanwhile, is subdivided into two groupings. The first contains 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 retain the generic name Rasbora as do clade five species because they don't differ sufficiently to warrant a the erection of a new genus/genera.

Unfortunately many species weren't included in the analysis, meaning inevitable questions are raised regarding the correct placement of the 40 or so other Rasboras, in particular. As the genus had previously been split into various 'species groups' (groups of closely-related species) 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 with further phylogenetic studies:

R. semilineata species group: R. semilineata, R. borapetensis , R. rubrodorsalis .
R. trifasciata species group: R. trifasciata, R. amplistriga, R. bankanensis, R. dies, R. ennealepis, R. hubbsi, R. johannae, R. meinkeni, R. paucisqualis, R. rutteni, R. sarawakensis , R. taytayensis, R. tobana, R. tuberculata.
R. daniconius species group: R. daniconius, R. caverii, R. kobonensis, R. labiosa, R. ornata, R. wilpita .
R. einthovenii  species group: R. einthovenii , R. cephalotaenia , R. elegans , R. jacobsoni, R. kalochroma , R. kottelati , R. nematotaenia, R. tubbi.
R. argyrotaenia  species group: R. argyrotaenia , R. aprotaenia, R. aurotaenia, R. baliensis, R. borneensis, R. bunguranensis, R. dusonensis , R. evereti, R. hobelmani, R. hossi, R. lateristriata, R. laticlavia, R. leptosoma, R. philippina, R. septentrionalis, R. spilotaenia, R. steineri, R. tawarensis, R. tornieri, R. volzii.
R. sumatrana species group: R. sumatrana, R. atridorsalis, R. calliura, R. caudimaculata , Rasbora dorsinotata, R. notura, R. paviana , R. rasbora , R. subtilis, R. trilineata , R. vulgaris.

Not classified: R. beauforti, R. chrysotaenia, R. gerlachi (validity in question), R. kalbarensis, R. reticulata, R. vulcanus  (possibly not Rasboras) and R. zanzibarensis (identity in question).

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. Howes (1980) suggested the separation of a number of species into the new genus Parluciosoma with type species P. (Rasbora) argyrotaenia but the monophyly of that grouping was not recovered by Liao et al.

Literature cited

1. 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 - J. Exp. Zool. (Mol. Dev. Evol.) 308B: 1–13.
   Phylogenetic relationships of Danio within the order Cypriniformes: a framework for comparative and evolutionary studies of a model species.
2. Kottelat, M. 1999 - Raffles Bull. Zool. 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.
3. www.petfrd.com