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Mesonoemacheilus triangularis (DAY, 1865)

Zodiac Loach

SynonymsTop ↑

Nemacheilus triangularis Day 1865; Noemacheilus triangularis (Day, 1865); Noemacheilus triangularis tambaraparniensis Menon, 1987


Mesonoemacheilus: from the Greek meso, meaning ‘half’, nema, meaning ‘thread, filament’, and cheilos, meaning ‘lip’, in reference to the relatively less deeply-furrowed lip in members compared to that in Nemacheilus spp.

triangularis: from the Latin triangulāris, meaning ‘triangular’, presumably in reference to the >-shaped markings on the flanks of the fish.


Order: Cypriniformes Family: Nemacheilidae


The type locality is given by Day as ‘the hills at Mundikyum’ which appears to correspond to the small town now known as Mundakayam, in Kottayam District of Kerala state, South India, through which runs the river Manimala.

Mundakayam lies within the Western Ghats mountains and M. triangularis has since been recorded to occur in river systems draining both sides of that range in the states of Kerala and Tamil Nadu, where it’s said to be locally abundant.


Inhabits clear, well-oxygenated, headwater streams and minor rivers. These are often shaded by surrounding forest cover with the substrate normally composed of coarse sandgravel, rocks and boulders covered with an epilithic layer of algaediatoms plus other microorganisms and detritus.

Aquatic plants usually absent, though Lagenandra and Blyxa spp. have been observed at some lower-gradient habitats.

Flow rate and turbidity vary somewhat depending on the time of year with both increasing dramatically during the annual monsoon season which occurs between June and September.

In the Panniyar river basin, Kerala it was collected alongside Haludaria fasciata, Tor khudree, Barilius bakeri, Devario aequipinnatus, Rasbora daniconius, Garra mcclellandi, Homaloptera santhamparaiensis, the congener Mesonoemacheilus guentheri and a Glyptothorax sp. during one study.

Maximum Standard Length

50 – 60 mm.

Aquarium SizeTop ↑

An aquarium with a base measuring at least 75 ∗ 30 cm is recommended.


Not difficult to maintain under the correct conditions; we strongly recommend keeping it in a tank designed to resemble a flowing stream or river with a substrate of variably-sized rocks, sand, fine gravel, and some water-worn boulders.

This can be further furnished with driftwood branches arranged to form a network of nooks, crannies, and shaded spots, thus providing broken lines of sight.

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

Though torrent-like conditions are unnecessary it does best if there is a high proportion of dissolved oxygen and some water movement in the tank meaning power filter(s), additional powerhead(s), or airstone(s) should be employed as necessary.

Like many fishes that naturally inhabit running water it’s intolerant to accumulation of organic pollutants and requires spotless water in order to thrive, meaning weekly water changes of 30-50% tank volume should be considered routine.

Water Conditions

Temperature18 – 25.5 °C

pH6.0 – 7.5

Hardness36 – 215 ppm


Mesonoemacheilus species are omnivorous although the bulk of their diet consists of small insects, worms, crustaceans and other zooplankton with only relatively small amounts of plant matter consumed.

In the aquarium they 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 DaphniaArtemiabloodworm, etc. will result in the best colouration and condition.

Behaviour and CompatibilityTop ↑

This species can apparently exhibit contrasting behaviour in captivity with some aquarists reporting it to be peaceful while others claim it to be territorial and aggressive.

It’s unknown if such differences relate to different wild populations, gender or some environmental variable but caution is recommended if introducing it to an established community.

UK aquarist Andy Rushworth found that transferring his previously combative M. triangularis to an entirely bare set-up resulted in a total loss of aggression though this option may of course not always be feasible or preferable.

At any rate, robust fishes which inhabit similar biotopes in nature, especially small, open water-dwelling cyprinids constitute the best options in terms of tankmates, with smaller species best omitted in shallower (<45 cm deep) tanks as they may prove unable to cope with persistent attacks.

Other possibilities include rheophilic loaches from genera such as Pseudogastromyzon, Beaufortia and Sewellia (avoid the more delicate genera, e.g., Gastromyzon) plus benthic cyprinds like Crossocheilus and Garra species.

Similarly-shaped relatives such as other NemacheilusAcanthocobitis and Schistura spp. are not really recommended although a combination may work in larger aquaria, while sedate bottom-dwellers such as Corydoras spp. catfishes are best omitted entirely.

This species is normally tolerant of conspecifics and seems to appreciate being maintained in a group, though as mentioned it can exhibit extreme territorial behaviour in some cases.

The purchase of four or more specimens is nonetheless recommended since observations of its native habitats suggest it occurs in quite large aggregations.

Sexual Dimorphism

Adult females are likely to grow slightly larger and be rounder-bellied than males when gravid.

Males have a small suborbital flap and may develop thickened pectoral-fin rays with rows of tubercules when sexually mature, as has been observed in M. herrei.


A single success was reported by an American aquarist in 2004.

An adult pair was removed from a community set-up containing several loach species and introduced to a 38 litre tank fitted with a small hang-on filter, the outflow of which was directed towards a plastic box filled with aquarium gravel.

Two large spawning mops were also added and weighed down using a piece of tile, and the author noted that the male was exhibiting reflective reddish-bronze colouration in the lower body and belly.

The male was however found dead the morning so a second individual was introduced since the female still appeared to be gravid.

The following day the fish were observed swimming up and down one side of the tank together, then entering one of the mops.

Close examination using a magnifying glass revealed ‘hundreds’ of clear, non-adhesive eggs on the base of the tank, and the adults were then removed after the male was seen eating them. Water temperature was 76°F/24.4°C.

The eggs were examined under a microscope at various stages of development and recorded to swell to a size of approximately 0.7 mm with a cellular cap apparent at just 3 hours of age.

Hatching seemingly began around 24 hours post-fertilisation, and once complete the mops, tub of gravel and hang-on filter were removed with the latter replaced by an air-driven sponge filter.

Once the first few fry showed signs of eye and intestinal development and had apparently consumed the yolk sac they were fed small amounts of ‘fry starter’, presumably a proprietary product, and by squeezing the sponge from a mature filter into the tank.

Artemia nauplii were introduced to the diet 24 hours later and progressively larger foods as the young fish grew. 500 individuals were eventually raised to saleable size.

NotesTop ↑

This species is also referred to by the alternative vernacular name ‘Batik loach’ and is relatively common in the aquarium trade.

It’s easily-distinguished from congeners by body patterning which comprises a series of pale, oblique saddle-like markings edged in black and running along the dorsal surface, plus a similar set of bars originating from the otherwise plain ventral surface.

The number and positioning of these is variable, and in some individuals they break up to an extent, forming additional blotches of random size, shape and number.

Older specimens tend to have more diverse patterning whereas in many younger fish the markings are conjoined forming a series of <-shaped bands.

With regard to the remaining members of the genus, only M. guentheri is regularly exported for the aquarium trade and is easily told apart since its body patterning comprises rows of yellowish, dark-edged spots, as does that of M. herrei.

M. petrubanarescui has dark body stripes, M. menoni a reticulated pattern of dark bands and blotches, M. pambarensis more branched dorsal-fin rays (8-10, usually 9, vs. 7-8 in M. guentheri) plus an elongate body the depth of which fits more than 5.5 times into the SL, M. pulchellus also has more branched dorsal-fin rays (always 10) and M. remadevii lacks dark markings in the fins.

All Mesonoemacheilus spp. are endemic to rivers draining the Western Ghats and the genus is separated from the closely-related Nemacheilus by members possessing two pairs of rostral barbels which are confluent at their bases vs. rostral barbels present but not confluent.

In addition, the lips are usually less deeply-furrowed in Mesonoemacheilus than Nemacheilus spp. while Bãnãrescu and Nalbant (1995) noted that Mesonoemacheilus is the only nemacheilid genus exhibiting a greater degree of brownish than whitish colouration.

According to Rema Devi and Indra (2002) Schistura savona from northern India uniquely shares both this feature plus possession of confluent rostral barbels and this may warrant further study, though it appears that this suggestion has not been followed to date.

The family Nemacheilidae is widely-distributed across most of Eurasia with the Indian subcontinent, Southeast Asia and China representing particular centres of species diversity.


  1. Day, F., 1865 - Proceedings of the General Meetings for Scientific Business of the Zoological Society of London 1865 (1): 286-318
    On the fishes of Cochin, on the Malabar Coast of India. Part II. Anacanthini.
  2. Arun, L. ., C. P. Shaji and P. S. Easa, 1996 - Journal of the Bombay Natural History Society 93(1): 103-104
    Record of new fishes from Periyar Tiger Reserve.
  3. Arunachalam, M., 2000 - Hydrobiologia 430: 1–31
    Assemblage structure of stream fishes in the Western Ghats (India).
  4. Boggs, S., 2004 - Finformation 57(7): 4-5
    Spawning the Batik Loach (Neomcheilus triangularis).
  5. Bãnãrescu, P. M. and T. T. Nalbant, 1995 - Travaux du Muséum d'Histoire Naturelle 'Grigore Antipa' 35: 429-495
    A generical classification of Nemacheilinae with description of two new genera (Teleostei: Cypriniformes: Cobitidae).
  6. Kottelat, M., 2012 - Raffles Bulletin of Zoology Supplement 26: 1-199
    Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei).
  7. Radhakrishnan, K.V. and B. Madhusoodana Kurup, 2010 - Journal of Threatened Taxa 2(10): 1192-1198
    Ichthyodiversity of Periyar Tiger Reserve, Kerala, India.
  8. Raju Thomas, K., M. J. George and C. R. Biju, 2002 - Journal of the Bombay Natural History Society 99(1): 47-53
    Freshwater fishes of southern Kerala with notes on the distribution of endemic and endangered species.
  9. Rema Devi, K. and T. J. Indra, 2002 - Journal of the Bombay Natural History Society 99(2): 333-337
    A note on Mesonoemacheilus herrei Nalbant and Banarescu (Cypriniformes: Balitoridae: Noemacheilinae).
  10. Shaji, C. P., 2002 - Indian Journal of Fisheries 49(2): 217-221
    Mesonoemacheilus remadevii (Pisces: Balitoridae. Nemeacheilinae) from Silent Valley National Park, Kerala.
  11. Tang, Q., H. Liu, R. Mayden and B. Xiong, 2006 - Molecular Phylogenetics and Evolution 39(2): 347-357
    Comparison of evolutionary rates in the mitochondrial DNA cytochrome b gene and control region and their implications for phylogeny of the Cobitoidea (Teleostei: Cypriniformes).
  12. Zacharias, V. J. and K. C. Minimol, 1999 - Journal of the Bombay Natural History Society 96(2): 288-290
    Noemacheilus menoni, a new species of fish from Malappara, Periyar Tiger Reserve, Kerala.
  13. Šlechtová, V., J. Bohlena and H. H. Tan, 2007 - Molecular Phylogenetics and Evolution 44(3): 1358-1365
    Families of Cobitoidea (Teleostei; Cypriniformes) as revealed from nuclear genetic data and the position of the mysterious genera Barbucca, Psilorhynchus, Serpenticobitis and Vaillantella.

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