Taxonomy & naming
Eirmotus insignis was described by Heok Hee Tan and Maurice Kottelat in 2008 as part of a revision of the genus Eirmotus — a small cluster of diminutive Sundaland barbs that had long been subsumed within the sprawling catch-all genus Puntius. The 2008 paper separated and redefined Eirmotus on morphological grounds, and E. insignis is one of three species erected or re-diagnosed in that work. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name Eirmotus insignis Tan & Kottelat, 2008.
The genus Eirmotus itself was originally erected by Hora in 1932, but fell into synonymy for decades as Puntius expanded to absorb most Indo-Malaysian small barbs; the Tan & Kottelat revision restored it. The broader reorganisation of Asian barb genera accelerated after Pethiyagoda et al. (2012) dismantled the old Puntius aggregate, and Eirmotus now sits as a valid, well-supported small genus of Sundaland barbs distinct from Puntius, Puntigrus, Pethia and their allies. The species epithet insignis is Latin for 'distinguished' or 'marked', likely a reference to the patterning that sets this species apart from its congeners.
Morphology
Eirmotus insignis is a small barb reaching approximately 1.5 in standard length. The body is slender and moderately compressed, typical of small Sundaland stream barbs. Coloration reflects the tannin-stained, turbid environments it inhabits: the flanks carry banding or spotting that gives rise to the common name 'false eight-banded barb', distinguishing it at a glance from the true eight-banded barbs while still echoing their patterned appearance.
Little detailed morphological data has been published outside the original description. As with many small Eirmotus, the species is likely sexually dimorphic to some degree — females becoming noticeably fuller-bodied when carrying eggs — though specific dimorphism notes are sparse in available hobbyist and scientific literature. The small adult size places it firmly in the nano fish category.
Habitat
Eirmotus insignis inhabits small, slow-flowing streams, backwaters and swampy areas within lowland rainforest on Borneo (Kapuas drainage, Kalimantan Barat, western Indonesian Borneo) and Belitung Island. These are Sundaland blackwater and slightly acidic clearwater environments — shallow, densely vegetated, often murky, with mud and leaf-litter substrates and heavy riparian shading. Water chemistry is soft to very soft, slightly to moderately acidic, characteristic of the peat-influenced lowland drainages of Sundaland.
SeriouslyFish reports water parameters of pH 5.0–7.0 and hardness of 18–143 ppm for this species, with temperatures of 68–79 °F. The slow-moving, shaded character of its habitat — dense submerged and marginal vegetation, turbid water, organic substrate — is markedly different from the faster hill-stream habitats of many other small Asian barbs, and it informs the specific aquarium conditions the species requires.
Feeding
In the wild, Eirmotus insignis is understood to feed on small invertebrates, algae and zooplankton gleaned from the substrate and water column in the dense vegetated margins of its stream and swamp habitats. Small chironomid larvae, Daphnia-type cladocerans and other microcrustaceans likely form the core animal component of its diet, supplemented by algal films and fine organic detritus — a feeding strategy typical of diminutive Sundaland barbs in slow, food-rich backwaters.
In aquaria the species accepts dried foods but shows a strong preference for live and frozen items. Daphnia and Artemia (brine shrimp) are particularly recommended by keepers. Given its small size and relatively retiring disposition, feeding alongside boisterous or fast-feeding tankmates risks competition that leaves E. insignis underfed; it fares best when food reaches it without contest.
Mating
Like all barbs, Eirmotus insignis is an egg-scattering, non-guarding spawner. No specialised mating system, nest construction or pair bond is known for this species. Courtship follows the typical barb pattern: a driving male pursues a gravid female through fine-leaved vegetation or over the substrate, the two pressing briefly together as eggs and milt are released simultaneously, after which each fish goes its own way.
Because the species lives in dense, shaded vegetation in slow backwaters, courtship in the wild likely takes place among submerged plants or over leaf-litter beds. Adults provide no care whatsoever to the eggs once deposited, and — as is characteristic of small barbs — will readily consume their own eggs if given the opportunity.
Breeding
Captive breeding of Eirmotus insignis has not been formally documented in the published hobbyist or scientific literature available — SeriouslyFish records it as 'unrecorded'. By analogy with closely related small Sundaland barbs, the species would be expected to scatter small adhesive eggs among fine-leaved plants or over a substrate of leaf litter, with no parental care whatsoever. Conditioning on live and frozen foods and the provision of soft, slightly acidic water matching wild parameters (pH 5.0–6.5, low hardness, 72–77 °F) would be the logical approach for any breeding attempt.
The small clutch sizes typical of nano barbs, combined with the absence of documentation, suggest this species remains a challenge for breeders. Anyone successfully spawning it in captivity would make a worthwhile contribution to the hobby literature.
In the aquarium
Eirmotus insignis is a specialist aquarium fish suited to quiet, species-specific or nano community set-ups rather than active general community tanks. It is a shoaling species requiring a group of eight to ten or more individuals to feel secure and display natural behaviour; kept in smaller numbers it becomes withdrawn and stressed. Boisterous or fast-moving tankmates are unsuitable companions.
The aquarium should replicate its natural habitat as closely as practical: soft, slightly acidic water (pH 5.0–7.0, low hardness), temperatures of 68–79 °F, subdued lighting, dense planting with fine-leaved species and floating cover, and a dark substrate of fine sand or leaf litter to reduce contrast and encourage the fish to show colour. Filtration should produce minimal current. It accepts dried foods but thrives when regularly offered live or frozen Daphnia and Artemia. The species is seldom available in the trade and appeals primarily to experienced keepers with an interest in authentic Sundaland biotope aquaria.
Conservation
Eirmotus insignis is assessed as Least Concern (LC) on the IUCN Red List (2019 assessment), based on its occurrence in both the Kapuas drainage of Kalimantan Barat (western Borneo) and on Belitung Island, and the absence of evidence of rapid population decline. It was included in the IUCN Red List Review and Assess-to-Plan (A2P) workshop for Sundaland freshwater fishes, which evaluated conservation priorities across the region.
Despite the Least Concern rating, the lowland rainforest streams and peat-swamp systems of Borneo and Belitung face severe and ongoing pressure: large-scale deforestation for palm oil and timber, peat drainage and burning, sedimentation, and water pollution all degrade the slow, clean, acidic habitats on which this species depends. Belitung Island has seen rapid development in recent decades. Although E. insignis has not been highlighted as an immediate extinction risk, the wholesale destruction of Sundaland peat-swamp forest represents a structural threat to the entire community of softwater stream fishes it represents.