This species is sometimes exported for the aquarium trade although normally only as by-catch among shipments of other species.
It's included in the P. kuhlii-oblonga group of closely-related species within the genus as per Bohlen et al. (2011) and can be distinguished from other members by the following combination of characters: plain, relatively deep body shape (body depth fits 8.0-9.6 times into SL); presence of nasal barbels; 45-49 vertebrae; emarginate caudal-fin; faint midlateral stripe sometimes present.
P. filinaris has apparently been confused with P. mariarum in the past by virtue of the fact the two share a plain body patterning and possess nasal barbels, and it's also been referred to by the invented name P. 'mariae'.
P. mariarum is endemic to northern Borneo and has probably never been exported for the aquarium hobby. It's also larger than P. filinaris, growing to at least 68 mm2.7 in SL, more slender (body depth fits 10.8-13.5 times into SL), has more pelvic-fin rays (6 vs. 5), more vertebrae (49-51 vs. 45-49), and in males the pectoral fins are noticeably curved upward (vs. not curved).
Kottelat and Lim (1993)[5] suggested that the P. kuhlii and P. oblonga groups represent two of four such assemblages within the genus alongside the P. anguillaris and P. shelfordii groups.
This unofficial system was followed until Bohlen et al. (2011) published a molecular phylogenetic analysis including 18 recognised species plus a number of undescribed ones.
Their results suggest the existence of three, rather than four, major lineages within the genus; the P. anguillaris and P. shelfordii groups represent two of them with Kottelat and Lim's P. kuhlii and P. oblonga groups together forming the third.
Within this third lineage are three sublineages formed by P. filinaris, an apparently undescribed fish from the Temburong River in Brunei referred to as P. cf. oblonga IV, and all other species in the group, respectively.
Species in the P. khulii and P. oblonga groups had previously been separated largely on the basis of colour pattern, i.e. barred vs. plain brown, but in the molecular analysis the barred species grouped within the brown. They also display a high degree of morphological affinity with simlarities in body shape and the number of vertebrae.
One brown specimen even grouped together with the barred P. malayana collected from the same locality rather than any of the other plain fish, suggesting a degree of phenotypic variability within species may also be involved.
Pangio is among the most speciose cobitid genera and widespread throughout South and Southeast Asia with species diversity thought to be considerably greater than currently recognised.
In the aquarium hobby Pangio species are often referred to generically as 'kuhli' or 'coolie' loaches, the latter a variation of the former which was itself derived from the surname of German naturalist Heinrich Kuhl (1797-1821). Ichthyologists tend to refer to them as 'eel loaches'.
They're distinguished from other cobitids by their long, slender body shape, relatively high number of vertebrae and the position of the dorsal-fin which is situated well behind the origin of the pelvic fins (vs. in front of, above or only slightly behind).
Several described members were previously included in the genus Acanthophthalmus which Kottelat (1987) demonstrated to be a syonym of Cobitis, and he chose the replacement name Pangio in preference to its simultaneous synonym Apua (Blyth, 1860).
Myers (1929) placed P. anguillaris as type species of Cobitophis, a grouping containing the very elongate species, while Perugia (1892) originally described P. doriae in the genus Eucirrhichthys. The former was synonymised with Acanthophthalmus by Nalbant (1963) and the latter by Roberts (1989).
The family Cobitidae, often referred to as 'true' loaches, is widely-distributed across most of Eurasia with the Indian subcontinent, Southeast Asia and China representing particular centres of species diversity.
Phylogenetic analyses by Tang et al. (2006), Šlechtová et al. (2007) and Šlechtová et al. (2008) revealed that the group constitutes a separate genetic lineage to the family Botiidae (the two were previously grouped together under Cobitidae as subfamilies Cobitinae and Botiinae).
In the most recent study Pangio was found to be more closely affiliated with Acantopsis, Acanthopsoides and Kottelatlimia than Lepidocephalichthys as had been previously hypothesised.
All cobitids possess sharp, motile, sub-ocular spines which are normally concealed within a pouch of skin but erected when an individual is stressed, e.g. if removed from the water. Care is therefore necessary as these can become entangled in aquarium nets and with larger species even break human skin.
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