Schistura oedipus (KOTTELAT, 1988)

SynonymsTop ↑

Noemacheilus oedipus Kottelat, 1988

Etymology

Schistura: from the Greek schizein, meaning ‘to divide’, and oura, meaning ‘tail’, in reference to the caudal-fin shape of many species.

oedipus: named for Oedipus, a mythic Theban king who tore out his eyes.

Classification

Order: Cypriniformes Family: Nemacheilidae

Distribution

Type locality is ‘Tham Nam Lang (Nam Lang Cave), 19°31’N, 98°09’E, Mae Hong Son Province, Thailand’, and this species is restricted to a series of caves in the Pang Mapha karst formation,  Mae Hong Son province, northwestern Thailand.

It’s known from five caves in total, the others being Tham Huet, Tham Ban Louk Kow Larm, Tham Nong Pha Cham, and Tham Mae Lana.

Streams flowing from these caves drain into the Nam Lang and Nam Khong rivers of the Salween drainage system, and the two easternmost caves, Tham Huet and Tham Nong Pha Cham, are both tributaries of the former.

They’re located 155 and 370 metres above river level, however, discharge into opposite shores of the Nam Lang and flow above ground for a distance before doing so, the latter limiting subterranean flow between them and thus contact between the two populations of fish.

The other three populations are also genetically-isolated, and analyses by Borowsky and Mertz (2005) revealed all five to be divergent from one another, forming three distinct groups.

The Nam Lang, Mae Lana and Ban Louk Kow Larm caves comprise one, while Tham Nong Pha Cham and Tham Huet are both unique.

These differences were not considered sufficient to designate them separate species, however, and it remains unresolved whether they derived from separate incidents of an ancestor invading caves, or from a single such event with subsequent isolation.

Habitat

Inhabits flowing subterranean streams which are often interrupted by cascades.

Maximum Standard Length

70 – 80 mm.

Aquarium SizeTop ↑

N/A

Maintenance

N/A

Water Conditions

Temperature: N/A

pH: N/A

Hardness: N/A

Diet

Said to feed on aquatic microorganisms and organic detritus.

Behaviour and CompatibilityTop ↑

N/A

Sexual Dimorphism

Males may possess a thickened second pectoral-fin ray (Kottelat, 1988).

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.

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

Troglomorphic fishes have been described from several familes with at least four other  blind loach species endemic to Thailand: Schistura deansmarti, S. oedipus , Nemacheilus troglocataractus ( all 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.

Schistura is the most species-rich genus among nemacheilid loaches with some 190 members and it continues to grow with over 100 having been described since 1990. It may represent a polyphyletic lineage and is often arranged into a number of loosely-defined species ‘groups’, some of which are quite dissimilar to one another.

Among these are an assemblage in which some or all of the body bars are vertically split and another which exhibit reductions in body size (adult size <50 mm SL), the number of pelvic and pectoral-fin rays and often the number of caudal-fin rays and lateral line length, for example.

Some species, such as S. geisleri, also appear to be unrelated to any of the others.

Most inhabit flowing streams or areas close to waterfalls where there naturally exist high concentrations of dissolved oxygen, and a handful are troglobytic, i.e., cave-dwelling, in existence. The latter have reduced pigmentation and are completely blind in many cases.

Schistura spp. are distinguished from other nemacheilids by a combination of morphological characters which include: a moderately arched mouth which is 2-3.5 times wider than it is long; a median ‘interruption’ in the lower lip which does not form two lateral triangular pads and can vary from smooth to furrowed in texture; diverse colour pattern but usually dark with relatively regular bars; usually a black bar at the caudal-fin base which can be broken into two spots or smaller bars; one or two black markings along the base of the dorsal-fin; lack of acuminate scales on the caudal peduncle; caudal-fin shape variable from truncate to forked but usually emarginate; presence or absence of a median notch in the lower jaw; clear sexual dimorphism in some species.

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

References

1. Kottelat, M., 1988 - Records of the Australian Museum 40(4): 225-231
   Two species of cavefishes from northern Thailand in the genera Nemacheilus and Homaloptera (Osteichthyes: Homalopteridae).
2. Borowsky, R. B. and L. Mertz, 2005 - Environmental Biology of Fishes 62: 225-231
   Genetic differentiation among populations of the cave fish Schistura oedipus (Cypriniformes: Balitoridae).
3. Bănărescu, 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).
4. Kottelat, M., 1990 - Verlag Dr. Friedrich Pfeil, München: 1-262
   Indochinese nemacheilines. A revision of nemacheiline loaches (Pisces: Cypriniformes) of Thailand, Burma, Laos, Cambodia and southern Viet Nam.
5. Kottelat, M., 2012 - Raffles Bulletin of Zoology Supplement 26: 1-199
   Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei).
6. 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.
7. 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).
8. Šlechtová, V., J. Bohlen 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.