T. heteromorpha was first exported for aquaria in the early 1900s and has gone on to become one of the most familiar, enduring species in the hobby.
It's suffered as a result of its popularity to a certain extent with the mass-produced fish we see today lacking much of the colour seen in wild specimens and even exhibiting morphological deformities in some cases.
Several selectively-bred ornamental strains have also become available including 'blue', 'black', and 'golden' (leucistic) forms, care for which is identical to the wild form.
It also appears that the species as currently recognised may contain multiple taxa with two divergent lineages found to be present among samples of fish from the aquarium trade by Collins et al. (2012).
Genetic differences were detected using a DNA barcoding technique but the two lineages also displayed morphological incongruities, with one form more slender, lacking a convex-shaped body profile posterior to the occiput, possessing less distinct pigmentation on the anterior dorsal and anal rays, and an additional orange/yellow anterior-subdistal blotch in the anal-fin.
This fish may turn out to be a so-called 'cryptic' or 'sibling' species and is labelled T. cf. heteromorpha in our images.
It can be confused with the similar-looking T. espei and T. hengeli although on close inspection they're actually quite easy to tell apart.
The basic body colouration of T. heteromorpha is pinkish, it has the deepest body shape of the three and the characteristic body marking is broader, more triangular in shape and darker in colour.
T. espei is generally a bright copper/reddish colour with a thinner, 'lambchop'-shaped body marking whereas T. hengeli is a slightly smaller fish with an overall greyish/colourless body colouration and a flash of bright orange pigmentation along the upper and anterior edges of the 'lambchop' marking.
T. somphongsi is the fourth, exceptionally rare, member of the genus but is very easy to distinguish from the others as the dark body marking is reduced to a thickish stripe.
The genus was erected by Kottelat and Witte (1999)[2] in order to separate members from the larger Rasbora grouping on the basis of the following combination of characters: colour pattern comprising a reddish, pinkish or orange body (in life) with a conspicuous black stripe extending from below dorsal-fin origin to middle of caudal-fin base and usually broadened anteriorly so as to have a triangular or hatchet shape (except in T. somphongsi in which the stripe is only slightly broader anteriorly); reproductive strategy in which eggs are deposited on the underside of broad leaves or similar structures.
Other characters distinguishing the genus (but not unique to it) are: miniature size (maximum 32 mm1.3 in SL in nature, though captive specimens may grow slightly larger); incomplete lateral line reduced to 6-9 pores; absence of barbels; 5 branched anal-fin rays; relatively deep body (not quantified).
Rasbora has 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 Boraras, Horadandia, Rasboroides, 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 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 (plus allies), R. kobonensis, R. ornata, and R. cf. daniconius.
Clade six 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 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.
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 genera Boraras and Trigonostigma.
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