Least rasbora
| Least rasbora | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Cypriniformes |
| Family: | Cyprinidae |
| Genus: | Boraras |
| Species: | B. urophthalmoides |
| Binomial name | |
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Boraras urophthalmoides (Kottelat, 1991) |
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The least rasbora or exclamation point rasbora (Boraras urophthalmoides) is a species of ray-finned fish in the genus Boraras. It was first described from a freshwater swamp associated with the Sai Buri River in Pattani province, southern (peninsular) Thailand, but currently considered to range throughout much of southern and central parts of the country, with the province of Narathiwat on the border, with Peninsular Malaysia appearing to represent the southern limit of its range.
Additional records are not extensive, but it seemingly occurs throughout the Mae Klong and Chao Phraya river basins and has been recorded in both Vietnam and Cambodia, where one notable population inhabits the moats and ponds of the Angkor Wat temple complex near Siem Reap.
It inhabits shallow bodies of water such as swamps, marshes, floodplains and rice paddies, where it is typically associated with submerged vegetation in predominantly clear water. It is also known to move into temporarily inundated areas during the wet season.
This species is very small, ranging from 12 to 16 mm.
Mature females are noticeably rounder-bellied and often a little larger than the slightly more colourful males.
This species appears to vary in colouration depending on collection locality, which has led to some confusion with B. brigittae as some populations can develop a strong orange/red stripe above the dark lateral marking when in good condition.
The least rasbora can be easily identified by its smaller adult size, distinct round, dark blotch on the caudal peduncle, comparatively long, unbroken lateral stripe and less uniformly red patterning. Its sometimes seen on sale under the trade names of ‘sparrow rasbora’ or ‘exclamation-point rasbora’, the latter in reference to the distinctive pattern formed by the dark body markings.
Boraras was erected in 1993 in order to separate a small group of species from the larger Rasbora assemblage on the basis of differences in morphology and reproductive strategy.
In older literature they are therefore referred to as members of Rasbora and following Liao et al. (2010) the genus is a member of the rasborin sub-group within the subfamily Danioninae (the other sub-group contains the danionins).
This group is further subdivided into six clades (clusters of closely related species), of which Boraras (or at least B. brigittae, the only species involved in the study) is included in ‘clade three’ alongside Horadandia atukorali, Rasboroides vaterifloris, Trigonostigma heteromorpha and three species previously included in Rasbora but moved into new genera by the authors: Trigonopoma gracile, T. pauciperforatum and Rasbosoma spilocerca.
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