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Petruichthys brevis (BOULENGER, 1893)

Inle Loach

SynonymsTop ↑

Nemachilus brevis Boulenger 1893; Eonemachilus brevis (Boulenger, 1893); Nemacheilus brevis Boulenger, 1893; Noemacheilus brevis Boulenger, 1893; Yunnanilus brevis (Boulenger, 1893)


Order: Cypriniformes Family: Nemacheilidae


Known only from the isolated mountain lake of Inle and surrounding watershed in Shan state, eastern Myanmar, and also occurs on the nearby He-Ho plain. Type locality is Fort Stedman on the lake’s eastern shore.

Lake Inle lies in a karstic valley known as the Yawnghwe basin located almost 900m above sea level in the Shan Plateau region and is home to many endemic animals including nine species of fish and numerous gastropods. It was originally much bigger and may originally have been more than 90 metres deeper than it is now.


The water in Lake Inle is clear, shallow (2-3 metres deep in most places) and has a very fertile, loamy substrate. It’s famed for its stilted villages and local fishermen known as Intha who row their boats using only one leg.

These people, thought to have migrated from the south of Myanmar in the late 1300s, use naturally-occurring floating ‘islands’ consisting of tangles of various plant species as gardens.

These islands form a wide raft around the lake margins and the Intha take them as required, removing the aerial leaves and cutting them into sections. Bamboo poles are added for support allowing fruit, vegetables, rice and flowers to be produced in commercial quantities.

The gardens rise and fall with the water level and have come to form the habitats of many fish which take shelter among the tangle of roots and plant stems at their base.

Macrophytes also grow densely in the crystal-clear water and include Ceratophyllum and Elodea-like species.

P. brevis is mostly collected around the margins of the lake where grass and reed-like plants proliferate and the floating islands form thick mats composed of both live and dead vegetation. Impossible to catch with a net, fishermen use special traps placed among the plants overnight.

As the lake is situated in a karstic zone it contains neutral to slightly alkaline water with the pH value varying between 7.5 – 8.0. Its main outlet is a seasonal stream known as the Balu Chaung which floods at certain times of year allowing the transfer of fishes to pools and ponds close to Loi Kaw.

During drier months these are disconnected, isolating small populations of several species. We’ve yet to obtain detailed information regarding these habitats but expect them to be characterised by similarly sluggish, clear water with dense marginal and submerged plant growth.

Maximum Standard Length

Males 35 – 40 mm, females 55 – 60 mm.

Aquarium SizeTop ↑

Base dimensions of 90 ∗ 30 cm or equivalent are required.


Best kept in a densely-planted tank and an excellent choice for the carefully-aquascaped set-up. The addition of some floating plants and driftwood roots or branches, and leaf litter also seems to be appreciated and adds a more natural feel.

If you wish to raise fry alongside the adults the addition of fine-leaved aquatic moss such as a Taxiphylum sp. is advisable (see ‘Reproduction’).

The water should be well-oxygenated but not turbulent though a degree of flow is acceptable. Do not add this fish to a biologically immature aquarium as it can be susceptible to swings in water chemistry, and be sure to perform regular partial water changes to maintain quality.

Water Conditions

Temperature: 20 – 26 °C

pH: 7.0 – 8.0. This species will not do well in acidic water.

Hardness215 – 357 ppm


Likely to be a micropredator feeding chiefly on small insects, worms, crustaceans, and other zooplankton in nature.

In the aquarium it must be offered items of a suitable size and quality , particularly live DaphniaMoinaArtemia nauplii, micro worm, etc. Small or crushed floating dried foods are also accepted and should ideally contain some plant or algal material.

Behaviour and CompatibilityTop ↑

Peaceful and likely to be intimidated or outcompeted for food by larger or more boisterous tankmates, although the presence of similarly-sized schooling fishes seems to help reduce its shyness.

Small cyprinids from genera such as BorarasMicrodevarioTrigonostigmaTanichthys, and Microrasbora are perhaps the best options, and we suspect many small characids would also be fine. Many peaceful loaches and catfishes should also prove suitable but as always research your choices thoroughly in order to avoid problems.
community based around fishes from Lake Inle would make an interesting project with species available in the trade including Danio erythromicronSawbwa resplendensDevario auropurpureusMicrorasbora rubescensPethia stoliczkana,  and Parambassis lala.

Yunnanilus spp. are highly gregarious and should be kept in a group of at least 8-10 specimens, ideally more.

Maintaining it in such numbers will not only make the fish less nervous but result in a more effective, natural-looking display. Unlike most loaches they also spend a lot of time in the open, often hovering in midwater and exploring all levels of the aquarium.

Sexual Dimorphism

Sexually mature females are usually rounder-bellied and noticeably larger than males with a colour pattern of irregular dark spots and small blotches, some of which may be fused to form small stripes or bars.

Males have a variable number of short, variably-sized vertical bars along the flanks, which in some specimens are joined to form a solid stripe, and also possess a suborbital flap which is absent in females.


Unrecorded as far as we know.

NotesTop ↑

This species is sometimes traded as ‘Lake Inle red-tailed loach’ and was formerly included in the genus Yunnanilus, a diverse assemblage of which the majority of members are endemic to the Yunnan plateau, Yunnan province, southern China.

A number of them are known only from a single locality or have very restricted ranges, and in some cases have come to colonise habitats or ecological niches not normally associated with nemacheilid loaches.

Several groups of closely-related species existing within Yunnanilus have been noted and Kottelat (2012) moved those that had been formerly included in the Y. nigromaculatus group into the genus Eonemacheilus Berg, 1938, while those from Myanmar were included in Petruichthys Menon, 1987.

Unfortunately we’ve yet to obtain the original descriptions of either of these revalidated genera, and no diagnoses were provided by Kottelat (2012), so we’re unable to provide distinguishing characters at this time.

P. brevis can however be told apart from congeners and related species by the following combination of characters: short lateral line with up to 12 pored scales; cephalic lateral line system present with 3+3 supratemporal and 9 pre0perculo-mandibular pores; 16-17 branched caudal-fin rays; caudal peduncle 1.06-1.14 times longer then deep; caidalñ peduncle depth 12-14% SL; eye diameter 6.2-7.6% SL; body depth 23-26% SL.

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. Boulenger, G. A., 1893 - Annals and Magazine of Natural History (Series 6) 12(69): 198-203
    List of the fishes collected by Mr. E. W. Oates in the southern Shan States, and presented by him to the British Museum.
  2. Bănărescu, P. M. and T. T. Nalbant, 1995 - Travaux du Muséum d'Histoire Naturelle : 429-495
    A generical classification of Nemacheilinae with description of two new genera (Teleostei: Cypriniformes: Cobitidae).
  3. Freyhof, J. and D. V. Serov, 2001 - Ichthyological Exploration of Freshwaters 12(2): 133-191
    Nemacheiline loaches from Central Vietnam with descriptions of a new genus and 14 new species (Cypriniformes: Balitoridae).
  4. Kottelat, M., 2012 - Raffles Bulletin of Zoology Supplement 26: 1-199
    Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei).
  5. Kottelat, M. and X.-L. Chu, 1988 - Environmental Biology of Fishes 23(1-2): 65-93
    Revision of Yunnanilus with descriptions of a miniature species flock and six new species from China (Cypriniformes: Homalopteridae).

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