Trigonopoma gracile

Cyprinidae

Native to Peninsular Malaysia, Singapore and the Greater Sunda Islands of Borneo and Sumatra. In Peninsular Malaysia it's widely-distributed having been collected in the states of Selangor, Terengganu, Johor and probably other areas containing peat swamp forest. Records from Singapore and Sumatra are poor and it's likely the species can no longer be found in the former. The only information pertaining to Sumatra we have is a single account from Natuna Besar, also known as Bunguran Island, one of the most northerly islands in Indonesia and part of the Riau Islands province. On Borneo the majority of collections have occured from the Kapuas River basin in the Indonesian province of West Kalimantan (Kalimantan Barat) and in neighbouring Central (Kalimantan Tengah). It also occurs in the Malaysian state of Sarawak but its range appears not to extend into the far north and east of the island.

Inhabits black water streams and rivers associated with ancient forest peat swamps. The water is stained brown due to the release of tannins and other chemicals released by decomposing organic matter and the substrate scattered with fallen leaves, twigs and branches. Such environments characteristically contain very soft (negligible hardness), acidic (pH as low as 4.0) water and are often dimly-lit due to the forest canopy above. Across much of Southeast Asia these biotopes are under threat from rubber/palm oil plantations, building developments and other human activities.

Fully-grown at around 2.2"/5.5cm.

A tank measuring 24" x 15" x 12"/60cm x 37.5cm x 30cm/70.8 litres is big enough to house a small group.

Choice of décor is not as critical as water quality although this species does look particularly effective in a well-planted tank with a dark substrate. To see it at its best a biotope-style set-up can also make an interesting project. A soft, sandy substrate is probably the best choice to which can be added a few driftwood roots and branches, placed in such a way that plenty of shady spots are formed. If you can't find driftwood of the desired shape common beech or oak is safe to use if thoroughly dried and stripped of bark.

The addition of dried leaf litter (beech, oak or Ketapang almond leaves are all suitable; we like to use a mixture of all three) would further emphasise the natural feel and as well as offering even more cover for the fish brings with it the growth of microbe colonies as decomposition occurs. These tiny creatures can provide a valuable secondary food source for fry whilst the tannins and other chemicals released by the decaying leaves are thought to be beneficial for blackwater fish species such as this. Certainly T. gracile is known to display more intense colouration in tannin-stained water. Leaves can be left in the tank to break down fully or removed and replaced every few weeks.

Allow the wood and leaves to stain the water. A small net bag filled with aquarium-safe peat can also be added to the filter or hung over the edge of the tank to aid in the simulation of black water conditions. Alternatively obtain some genuine peat fibre and simply drop a few handfuls into the tank. This will become completely saturated with water after a few days and sink to the bottom where it can look really effective. Provided a good routine of water maintenance is practiced no adverse effects should occur using either peat or leaves in an aquarium.

Fairly dim lighting is also preferable. You could add some aquatic plants that can survive under such conditions such as Microsorum pteropus, Taxiphyllum barbieri or perhaps some potted Cryptocorynes. A few patches of floating vegetation would be really useful to diffuse the light entering the tank too. Do not add this fish to a biologically immature tank as it can be susceptible to swings in water chemistry and be sure to add a tightly-fitting cover as like most rasboras it is an accomplished jumper.

73 - 79°F/23 - 26°C

5.0 - 7.0

1 - 10°H

Likely to be a micropredator feeding on small insects, worms, crustaceans and other zooplankton in nature. In the aquarium it will 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, Artemia along with good quality flakes and granules will result in the best colouration and encourage the fish to come into breeding condition.

This species makes an ideal addition to a peaceful community of Southeast Asian/Indian species such as similarly-sized Rasbora, Puntius, botiid/cobitid loaches and gouramis of the genus Trichogaster. In a biotope set-up you could try it alongside other Malaysian or Bornean blackwater species. There are many suitable choices but some of the more commonly exported examples include Puntius lineatus , P. pentazona , Trigonopoma pauciperforatum , Rasbora einthovenii  and Pangio loaches. It also makes an ideal companion for shy anabantoids such as Sphaerichthys or the more diminutive Betta species.

It's a schooling species by nature and really should be kept in a group of at least 8-10 specimens. Maintaining it in decent numbers will not only make the fish less nervous but will result in a more effective, natural-looking display. Males will also display their best colours as they compete with one other for female attention.

Mature females are noticeably rounder-bellied and often a little larger than males.

Like many small cyprinids this species 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. The adult group can still be conditioned together but one or more long, shallow, say 30" x 12" x 12"/75cm x 30cm x 30cm/71 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. The water itself should be of slightly acidic pH with a temperature towards the upper end of the range suggested above. A small 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. Several spawning events will usually occur before a female is spent of eggs.

The adults will 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 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 Paramecium or similar introducing Artemia nauplii and/or microworm once the fry are large enough to accept them.

This species occurs in several colour forms depending on collection locality with some exhibiting more intense red colouration in the fins or a second, reddened lateral stripe, for example. It's sometimes said to closely resemble and occur sympatrically with Rasbora agilis, but despite being listed as valid by some sources the latter is a junior synonym of both T. gracile and T. pauciperforatum . R. agilis had previously been used to refer to a fish described by Ahl as R. taeniata and redescribed as R. gracilis by Kottelat in 1991 because the type specimens were found to represent a different genus. It was pictured in a 1971 book by Brittan labelled as R. agilis and this is probably where most of the confusion originated. It's quite common in the trade and is collected from the same waters as T. pauciperforatum  (also often referred to as R. agilis) across much of its range, so it seems that the R. agilis name has only been perpetuated via cases of misidentification. Any fish seen on sale as such are almost certain to be T. gracile or T. pauciperforatum .

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 , R. 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, Richard L.; Tang, Kevin L.; Conway, Kevin W.; Freyhof, Jörg; Chamberlain, Sarah; Haskins, Miranda; Schneider, Leah; Sudkamp, Mitchell; Wood Robert M.; Agnew, Mary; Bufalino, Angelo; Sulaiman, Zohrah; Miya, Masaki; Saitoh, Kenji; He, Shunping. 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. R. Zakaria, M. Mansor and A.B. Ali. 1999 - Wetlands Ecology and Management 6(4): 261-268.
   Swamp-riverine tropical fish population: a comparative study of two spatially isolated freshwater ecosystems in Peninsular Malaysia.
4. www.fishbase.org