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Acrochordonichthys gyrinus VIDTHAYANON & NG, 2003


Order: Siluriformes Family: Akysidae


Described and known only from the Yom River in Phitsanulok Province, northern Thailand, the major tributary of the Nan River within the upper Chao Phraya drainage basin.


According to Ng and Ng (2001) the congener A. rugosus inhabits fast-flowing forest streams containing transparent water with substrates of sand or rocks with some patches of leaf litter, and tends to congregate under submerged driftwood or rocks. Acrochordonichthys spp. appear to be largely nocturnal based on observations both in captivity and the field.

Maximum Standard Length

70 – 80 mm.

Aquarium SizeTop ↑

This species isn’t particularly active but a tank with base measurements of at least 75 cm x 30 cm is recommended since fluctuating water chemistry, typical of small aquaria, is unlikely to be tolerated long-term.


Most importantly the water must be clean and well-oxygenated so we suggest the use of an over-sized filter as a minimum requirement. Installation of a rivertank manifold would provide a suitable alternative form of filtration and bring with it the benefit of unidirectional water movement, though in reality provided the water contains plenty of dissolved oxygen the method used to achieve it is irrelevant, meaning air stones, oxidating devices, etc. can all be employed as you wish.

Base substrate can comprise fine gravel, sand or a mixture of both to which can be added a layer of water-worn rocks and pebbles of varying sizes, plus a few handfuls of leaf litter if you prefer. Aged driftwood and roots are also suitable and though not a feature of the natural habitat aquatic plants can be used with hardier species such as Microsorum pteropus (Java fern), Crinum and Anubias spp. likely to fare best. This species requires stable water chemistry so should never be added to immature set-ups, and regular partial water changes in the region of 30-50% tank volume per week are also essential.

Water Conditions

Temperature: 17.5 – 24 °C

pH: 5.0 – 7.0

Hardness: 0 – 179 ppm


Acrochordonichthys spp. are ambush predators by nature and Ng and Ng (2001) report that an adult specimen collected in the state of Terengganu, Peninsular Malaysia regurgitated three individuals of a Nemacheilus and one of a Glyptothorax sp.. In the aquarium there’s no need to feed live fishes since live or frozen invertebrates such as chronomid larvae, Tubifex and small earthworms are normally accepted without issue, though you may have to drop the food directly in front of the fish to provoke a response. Such targeted feeding will probably be mandatory in a community setting since these catfishes are sedentary and make poor competitors.

Behaviour and CompatibilityTop ↑

There is an inherent chemical risk in maintaining members of this genus alongside other species (see ‘notes’) and smaller tankmates will obviously be consumed, so they aren’t particularly recommendable community fishes. Larger set-ups containing schools of sufficiently-sized, non-aggressive species which enjoy slightly cool, flowing water such as many members of Devario or the Rasbora sumatrana species group thus constitute the most sensible choices. Other substrate-dwellers can also be kept provided they’re large enough to evade predation and non-territorial. Though not really gregarious this species is not aggressive towards conspecifics too large to swallow and can therefore be maintained in a group.

Sexual Dimorphism

In males the anus is situated immediately anterior to the genital papilla, which is itself positioned posterior to the pelvic fin base. There is an opening at the tip of the papilla which is covered by a flap of skin. In females the anus is located more poteriorly and the papilla consists oh a short tube with an opening at the tip without a fleshy flap.


No records of captive breeding exist and little is known of its natural behaviour.

NotesTop ↑

As in other members of the genus body colouration in this species is variable, even among individuals collected from a single locality, although a few regularities have been observed which can be used to distinguish certain species from one another. This is thought related to the fact that Acrochordonichthys spp. periodically shed their skins and appear paler post-moulting.

A. septentrionalis is a member of the so-called A. ischnosoma group within the genus, one of two assemblages recognised by Ng and Ng (2001) who noted that although possibly artificial such an arrangement provides assistance when discussing taxonomic relationships between the various species. It contains those species possessing a relatively slim caudal peduncle (depth 4.7-5.3% of standard length), narrower head (width 18.3-21.9% of standard length) and 39-41 vertebrae and currently comprises A. ischnosoma, A. guttatus, A. gyrinus, A. mahakamensis, A. septentrionalis and A. strigosus.

The second assemblage is referred to as the A. rugosus group and composed of species with a deeper caudal peduncle (depth 5.5-8.8% of standard length), wider head (width 22.0-29.6% of standard length) and 35-37 vertebrae. Constituent species at time of writing are A. rugosus, A. chamaeleon, A. falcifer and A. pachyderma.

Among the former group A. gyrinus differs from all other members by the shape of the posterior margin of the pectoral fins which is concave (vs. straight in all other A. ischnosoma group species). There is less distance between dorsal and adipose fins than in A. ischnosoma (7.4-8.6% of standard length vs. 9.0-10.1), the body is slimmer than that of A. guttatus (body depth at anus 8.3-10.5% of standard length vs. 10.9-12.8%) and the humeral process thicker (maximum breadth 16.3% of its length vs. 10.0-11.8). It differs from both A. mahakamensis and A. strigosus by exhibiting a straight (vs. rounded) posterior margin of the adipose fin and from A. septentrionalis by its flatter head (depth 9.8–11.4% of standard length vs. 12.8–13.6%).

Acrochordonichthys spp. possess some interesting adaptations, the most conspicuous of which is the ability to secrete a milky substance from the axillary pore located just below the humeral process (above the base of the pectoral fin). This discharge has not been studied in detail but appears to be a defensive mechanism since it can quickly kill other fishes in a confined environment such as an aquarium and is only produced when an individual is stressed in some way. Below the pectoral fin base the gill opening forms a specialised spout-like arrangement which is apparently related to locomotion, water being channeled through it in order to push the fish forwards in a similar fashion to members of the family Aspredinidae.

In terms of phylogenetics the family Akysidae is considered most closely related to the families Sisoridae, Amblycipitidae and Erethistidae with these four forming a monophyletic clade sister to the Bagridae.


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    A revision of the akysid catfish genus Acrochordonichthys Bleeker.
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    Acrochordonichthys gyrinus, a new species of akysid catfish (Teleostei: Siluriformes) from Thailand.

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