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Nemacheilus troglocataractus KOTTELAT & GÉRY, 1989


Nemacheilus: from the Greek nēma, meaning ‘thread’ or ‘filament’ and cheilos, meaning ‘lip’ in reference to the furrowed lip in members of this genus.

troglocataractus: from the Greek trôglê, meaning ‘hole’. and Latin cataracta, meaning ‘waterfall’. The latter is in reference to Nam Tok, the closest populated place to the type locality, while an alternative name for the cave (see ‘Distribution’) also translates as ‘waterfall’.


Order: Cypriniformes Family: Nemacheilidae


Known only from a single cave system (Tham Sai Yok Noi) near the town of Nam Tok Sai Yok Noi, Sai Yok district, Kanchanaburi Province, Thailand.

The headwater stream running through the cave is part of the Khwae Noi river basin, itself a tributary of the upper Mae Klong system.

Caves in Thailand often have several different names and Tham Sai Yok Noi is also known as Tham Wang Badan, Tham Vang Ba Dahl or Tham Nam Tok.

The cave is popular with tourists with the stream accessible by a small hole but apparently difficult to explore due to high carbon dioxide levels (Trajano et al., 2002).


621 metres of the cave system has reportedly been explored but its full extent remains unknown. The habitat is entirely subterranean and substrate composed largely of bedrock with some gravel in shallower areas.

Water flow is relatively slow and the stream is broken up by numerous small pools. Brouquisse and Dalger (1987) reported water parameters including temperature 76.1°F/24.5°C, pH 6.25, total hardness 22.6° dH, carbonate hardness 21.2° dH and conductivity 481 µS.cm.

Several fish species with epigean morphology have been observed in the cave along with a species of Machrobrachium shrimp plus a hypogean population of the catfish Pterocryptis buccata. Trajano et al., 2002 reported that N. troglocataractus population density seemed low and recorded only a few individuals which were found both on rocks in highly-oxygenated, flowing water and in the small pools.

They further commented that this is possibly due to an artificial reduction in numbers caused by collection of the species for the aquarium trade but that it’s impossible to accurately predict population size with the information available.

It’s officially protected under Thai law and currently considered ‘vulnerable’ by the IUCN but has not been assessed since 1996, but the Thai Fisheries Department classify it as ‘critically endangered‘.

Maximum Standard Length

60 – 68 mm.

Aquarium SizeTop ↑




Water Conditions

Temperature: N/A

pH: N/A

Hardness: N/A


Unconfirmed but likely to consist largely of benthic invertebrates.

Behaviour and CompatibilityTop ↑

This species is apparently territorial to an extent with specimens maintained together in aquaria exhibiting a degree of aggression towards one another.

This behaviour is exemplified by the dominant fish switching to a ‘zig-zag’ swimming action along with both lateral and ventral ‘shoving’ and biting.

Sexual Dimorphism



Unrecorded in aquaria and no reports exist regarding the natural cycle. A typical life cycle adaptation recorded in other cave-dwelling fish species is the production of precocial phenotypes, i.e., fewer, larger eggs that develop relatively slowly.

On hatching the fry are thus comparatively well-developed and better able to forage for food immediately.

NotesTop ↑

This species’ conservation status clearly precludes its suitability as an aquarium fish so it’s included here for reasons of interest only.  It’s protected by Thai national law and illegal to remove from its habitat.

Some aspects of the pleural rib morphology show similarities to those seen in N. fasciatus, N. masyae and N. pallidus. The latter pair occur in the same river system and may be closely related.

Species exhibiting morphological, physiological or behavioral adaptations to a subterranean existence are often referred to as troglomorphic.

In N. troglocataractus the majority of specimens have no externally visible eyes, though in at least one individual examined a single vestigial eye remained, and all are entirely depigmented.

Troglomorphic fishes have been described from several familes with at least four other blind loach species endemic to Thailand: Schistura deansmarti, S. jarutanini, S. oedipus (Nemacheilidae) and Cryptotora thamicola (Balitoridae).

Troglomorphic fish species may also be referred to as hypogean or troglobitic, and are often characterised by certain aspects of their ecology including low population size, restricted distribution, low tolerance to environmental degradation, precocial life cycle traits, a lack of environmental cues, restricted space and frequent scarcity of food (Trajano, 2001).

They’ve been found in all continents except Europe with the majority representatives of the orders Cypriniformes and Siluriformes.

Following Kottelat (1990) the genus Nemacheilus is characterised by a combination of characters as follows: elongate body; complete lateral line; presence of enlarged scales above and below the lateral line in some species; caudal-fin forked to deeply forked with enlarged upper lobe; large eye; small, strongly arched mouth; lips usually thin; usually no median interruption in upper lip; upper jaw with processus dentiformis (a tooth-like projection); no median notch in lower jaw; long barbels; males usually with suborbital flap, pectoral-fin rays 2-6 thickened and with rows of tubercules.

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. Kottelat, M. and J. Géry, 1989 - Spixiana 11(3): 273-277
    Nemacheilus troglocataractus, a new blind cavefish from Thailand. (Osteichthyes, Balitoridae).
  2. Kottelat, M., 2012 - Raffles Bulletin of Zoology Supplement 26: 1-199
    Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei).
  3. Kottelat, M., 1990 - Verlag Dr. Friedrich Pfeil, München, Germany: 1-262
    Indochinese nemacheilines. A revision of nemacheiline loaches (Pisces: Cypriniformes) of Thailand, Burma, Laos, Cambodia and southern Viet Nam.
  4. Kottelat, M., 2013 - Raffles Bulletin of Zoology Supplement No. 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. Ng, H. H. and M. Kottelat., 1998 - Ichthyological Research 45(4): 393-399
    Pterocryptis buccata, a new species of catfish from western Thailand (Teleostei: Siluridae) with epigean and hypogean populations.
  6. Proudlove, G. S., 2001 - Environmental Biology of Fishes 62(1-3): 201-213
    The conservation status of hypogean fishes.
  7. Romero, A. and K. M. Paulson, 2001 - Environmental Biology of Fishes 62(1-3): 13-41
    It's a wonderful hypogean life: a guide to the troglomorphic fishes of the world.
  8. Trajano, E., 2001 - Environmental Biology of Fishes 62(1-3): 133-160
    Ecology of subterranean fishes: an overview.
  9. Trajano, E., N. Mugue, J. Krejca, C. Vidthatayanon, D. Smart and R. Borowsky, 2002 - Ichthyological Exploration of Freshwaters 13(2): 169-184
    Habitat, distribution, ecology and behavior of cave balitorids from Thailand (Teleostei: Cypriniformes).

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