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Opsarius caudiocellatus (CHU, 1984)

SynonymsTop ↑

Barilius caudiocellatus Chu, 1984


Opsarius: apparently from an Ancient Greek word meaning ‘small fish’.

caudiocellatus: from the Latin cauda, meaning ‘tail’, and ocellus, meaning ‘little eye’, in reference to the eye-like marking on the caudal-fin base of this species.


Order: Cypriniformes Family: Cyprinidae


Known only from the Salween River system in southern China, Myanmar, and western Thailand, plus the upper Mekong basin in Yunnan province, China. In the latter country the Salween and Mekong are known as the Nu Jiang and Lancang Jiang, respectively.

Type locality is ‘Mengding, 23°33’N, 99°05’E, Salwin drainage, China’.


The information available suggests it to inhabit well-oxygenated, low-to-medium gradient, moderate to fast-flowing rivers and streams with substrates of gravel, cobbles, larger boulders and exposed bedrock.

Syntopic species include Abbottina rivularisSchistura latifasciata, Garra mirofrontis, and Pseudorasbora parva.

At one habitat in the Beiqiaohe River, Luozhahe River subbasin, Mekong basin, Yunxian County, Yunnan the water was turbid, had a temperature of 22 ºC at 20 cm depth, a pH of 7.6, and conductivity 70 µS/cm in January 2010 (M. Endruweit, pers. comm.).

Maximum Standard Length

The largest officially-recorded specimen measured 86 mm.

Aquarium SizeTop ↑

Likely to require a large aquarium with dimensions in the region of 150 ∗ 45 cm.


The aquarium should ideally be designed to resemble a flowing stream or river with a substrate of variably-sized rocks, sand, fine gravel, and some larger water-worn boulders. This can be further furnished with driftwood roots and branches if you wish but be sure to leave plenty of open swimming space.

While the majority of aquatic plants will fail to thrive in such surroundings hardy genera such as Microsorum, Bolbitis, or Anubias spp. can be grown attached to the décor.

This species is intolerant to the accumulation of organic wastes and requires spotless water at all times in order to thrive. It also does best if there is a high proportion of dissolved oxygen and moderate degree of water movement meaning external filters, powerheads, airstones, etc., should be employed as necessary.

As stable water conditions are obligatory for its well-being this fish should never be added to biologically-immature aquaria, and weekly water changes of 30-50% aquarium volume should be considered mandatory. A tightly-fitting cover is also essential as Opsarius spp. are prodigious jumpers.

Water Conditions

Temperature18 – 24 °C

pH6.5 – 8.0

Hardness36 – 215 ppm


Opsarius spp. are predominantly surface-feeders preying on aquatic and terrestrial insects in nature, with some small fishes and benthic invertebrates probably taken as well.

In the aquarium good quality dried products can be offered but should be supplemented with regular meals of live and frozen fare such as chironomid larvae (bloodworm), Artemia, chopped earthworms, etc. Drosophila fruit flies and small crickets are also suitable provided they are gut-loaded prior to use.

Behaviour and CompatibilityTop ↑

Unsuitable for the general community due to its environmental requirements, and likely to outcompete or intimidate slow-moving and less bold species at meal times since it is an extremely fast swimmer and vigorous feeder. Much smaller fishes should also be omitted as they may be predated upon.

The best tankmates are similarly-sized, robust, pelagic cyprinids such as Dawkinsia, Barilius or larger Devario and Rasbora spp. while bottom-dwellers could consist of Garra, Crossocheilus, Botia and Schistura spp., for example. Many characids and loricariid catfishes should also work well, but be sure to perform thorough research before purchase.

Although gregarious by nature this is a shoaling rather than schooling species which develops a distinct pecking order and therefore should always be maintained in a group of five or more individuals. If only two or three are purchased the subdominant fish may be bullied incessantly whereas solitary specimens may become aggressive towards similar-looking species.

Sexual Dimorphism

Adult females are likely to be less-brightly-coloured, grow a little larger and be thicker-bodied than males, especially when gravid.

Nuptial males may develop breeding tubercules and intensify in colour as in related species.



NotesTop ↑

This species may have appeared in the aquarium trade though probably not under the correct name.

It can be told apart from similar-looking congeners by the following combination of characters: presence of a black round spot at the caudal base; dorsal-fin rays black with connecting membranes transparent; posterior dorsal-fin origin located midway between upper angle of gill aperture and caudal-fin base, or slightly closer to the latter.

The generic placement of species currently referred to Opsarius has been open to question since Howes (1980) concluded that the Barilius grouping, within which they were included at the time, was not monophyletic and identified two separate lineages. The first group contained B. barila, the type species, plus B. bendelisisB. radiolatusB. vagra, and B. shacra, while the second included all other species, and initially these were referred to the subdivisions ‘group i’ and ‘group ii’ within Barilius itself.

The composition of these groups is confusing since in a later work Howes (1983) included B. evezardi and B. modestus in ‘group i’ whilst omitting B. bendelisisB. radiolatus, and B. shacra without explicitly stating why.

Rainboth (1991) assigned the members of Howe’s ‘group ii’ to the revalidated generic name Opsarius based on the fact it was the oldest available with ‘group i’ species retaining the name Barilius due to the presence of the type species.

This system has been followed by some subsequent authors, e.g., Tang et al. (2010) and Collins et al. (2012) but not gain wider usage until Kottelat (2013), who included all former Barilius from Southeast Asia in Opsarius.


  1. Chu, X-L, 1984 - Zoological Research 5(1): 95-102
    Provisional revision of the genus Barilius in China (Pisces: Cyprinidae).
  2. Endruweit, M. (ed), 2012 - World Wide Web electronic publication, www.aquariophil.org: Accessed on 12.10.04
  3. Howes, G. J., 1980 - Bulletin of the British Museum (Natural History) : Zoology series 37(3): 129-198
    The anatomy, phylogeny and classification of bariliine cyprinid fishes.
  4. Kottelat, M., 2013 - Raffles Bulletin of Zoology Supplement 27: 1-663
    The fishes of the inland waters of southeast Asia: a catalogue and core bibiography of the fishes known to occur in freshwaters, mangroves and estuaries.
  5. Liao, T-Y, S. O. Kullander, and F. Fang, 2011 - Journal of Zoological Systematics and Evolutionary Research 49(3): 224-232
    Phylogenetic position of rasborin cyprinids and monophyly of major lineages among the Danioninae, based on morphological characters (Cypriniformes: Cyprinidae).
  6. Nath, P., D. Dam, and A. Kumar, 2010 - Records of the Zoological Survey of India 110(3): 19-33
    A New Fish Species of the Genus Barilius (Cyprinidae: Rasborinae) from River Siang, D'Ering Memorial Wildlife Sanctuary, Arunachal Pradesh, India.
  7. Tang, K. L., M. K. Agnew, W. J. Chen., M. V. Hirt, T. Sado, L. M. Schneider, J. Freyhof, Z. Sulaiman, E. Swartz, C. Vidthayanon, M. Miya, K. Saitoh, A. M. Simons, R. M. Wood, and R. L. Mayden, 2010 - Molecular Phylogenetics and Evolution 57(1): 189-214
    Systematics of the subfamily Danioninae (Teleostei: Cypriniformes: Cyprinidae).

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