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Eirmotus octozona SCHULTZ, 1959

Classification

Order: Cypriniformes Family: Cyprinidae

Distribution

The type series consisted of aquarium specimens apparently originating from a lake named Bueng Boraphet in central western Thailand, but despite extensive sampling of the region in the years since this species has never been recorded there.

Specimens used in Tan and Kottelat’s 2008 revision of the genus were also obtained from the aquarium trade but appeared to come from western Peninsular Malaysia. The authors subsequently suggested that if it does occur in Thailand it’s likely restricted to the southern, peninsular section.

Information obtained from a collector in the same study hints that it was once found in areas of peat swamp forest around the town of Ayer Hitam in Johor state, Peninsular Malaysia along with other species of mysterious origin such as Gymnochanda filamentosa. The peat swamps in this area have been severely disturbed with many of the original habitats destroyed so the current status of the species is best described as unclear. It’s possible that some of the fish imported for the hobby as E. octozona are actually E. insignis.

Habitat

Unconfirmed. Other members of the genus variously inhabit shady, slow-moving forest streams with dense marginal vegetation, leaf litter/mud substrates and slightly acidic water or heavily-vegetated swamps (E. insignis), peat swamp forests (E. furvus) or flood plains and the margins of lakes (E. isthmus).

Maximum Standard Length

Around 1.4″/3.6cm.

Aquarium SizeTop ↑

An aquarium with a base measuring 60 ∗ 30 cm or larger is recommended.

Maintenance

Will thrive in a heavily-planted or forest stream-type set-up, the latter comprising a soft substrate, dim lighting, roots, branches and leaf litter as décor. You could also add aquatic plants that can survive under such conditions such as MicrosorumTaxiphyllum or Cryptocoryne spp. Filtration does not need to be particularly strong as it mostly hails from sluggish waters.

Eirmotus species can be tricky to acclimatise to captive life as they often arrive in poor condition and seem sensitive to fluctuating water chemistry. Never introduce them to biologically-immature aquaria and perform small, regular water changes of around 10% tank volume.

Water Conditions

Temperature22 – 26 °C

pH5.0 – 7.0

Hardness0 – 143 ppm

Diet

Likely to feed on small invertebrates, algae 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 DaphniaArtemia and suchlike will result in the best colouration and encourage the fish to come into breeding condition.

This species can be quite weak on import and small live foods are highly recommended as an initial diet, introducing the dry and frozen products as the fish become settled. It’s also noted as something of a shy, even reluctant, feeder.

Behaviour and CompatibilityTop ↑

Unsuitable for most community aquaria as it may be intimidated or outcompeted for food by larger or more boisterous tankmates. Small, peaceful cyprinids such as Trigonostigma or Boraras species are suitable companions and we suspect it will also do ok with many small South American characins, Otocinclus or pygmy Corydoras catfishes.

Accommodating it in a biotope-style community of Malaysian species is also a possibility with some of the more suitable ones including Trigonostigma heteromorpha, Boraras maculatus, Danio albolineatus, D. kerri, ‘Puntius partipentazona, Brevibora dorsiocellata, Trigonopoma gracile, T. pauciperforatum, and Acanthopsoides molobrion plus various Nemacheilus, Pangio, and Homaloptera spp.

It’s a shoaling 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 and some interesting behaviour as they compete with one other for female attention.

Sexual Dimorphism

Adult males are noticeably slimmer than females and exhibit a pale red colouration in the unpaired fins when in good condition.

Reproduction

Unrecorded as far as we know.

NotesTop ↑

Prior to revision by Tan and Kottelat (2008) the genus was monotypic for almost 50 years, with E. octozona the sole representative. There now exist four species all of which uncommon in the aquarium hobby and very similar in appearance.

E. octozona can be told apart from congeners by the following combination of characters: bar 1 present; presence of a large and distinct black mark anterior to anus, visible in lateral and ventral views; simple dorsal-fin rays black, sometimes extending onto first branched ray; other rays hyaline or with diffused chromatophores on last dorsal-fin ray, adjacent to upper extremity of bar 6; 25-31 serrae on last simple dorsal-fin ray; uppermost ray of pectoral-fin with faint black margin; width of bar 5 equal to 1-1½ lateral row scales; mouth terminal, lower jaw wide, rounded anteriorly.

The numbered bars mentioned here refer to the black body bars which the authors ordered from 1 to 8 beginning with the anteriormost one across the snout and ending with the small bar across the caudal peduncle. This patterning also gave rise to the common/trade name of ‘false eight-banded barb‘ under which both E. octozona and E. insignis can sometimes be seen on sale.

Members of this genus possess rows of sensory papillae on the snout, cheeks, throat, opercle and interorbital area that are lacking in most other cyprinids but present in a few other genera including Oreichthys, Cyclocheilichthys, Neobarynotus and a handful of other species. They are further characterised by a small adult size of less than 36mm SL, body patterning consisting of eight dark bars on a red to yellowish background, relatively large scales, an incomplete lateral line with only 2-6 perforated scales, serrations on the last simple dorsal ray and a lack of barbels.

References

  1. Tan, H.H. and M. Kottelat, 2008 - Raffles Bulletin of Zoology 56(2): 423-433
    Revision of the cyprinid fish genus Eirmotus, with description of three new species from Sumatra and Borneo.

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