Acrochordonichthys septentrionalis NG & NG, 2001

Mae Klong Chameleon Catfish

Etymology

Acrochordonichthys: from the Greek akrochordón (Gr. ἀκροχορδών), meaning ‘wart’, referring to the tuberculate skin of type species A. rugosus, plus ichthýs (Gr. ἰχθύς), meaning ‘fish’.

septentrionalis: Latin term for ‘northern’, in reference to this species being the most northerly-distributed member of the A. ischnosoma species group.

Classification

Order: Siluriformes Family: Akysidae

Distribution

Described from the Khwae Noi River (often referred to as the River Kwai) in Kanchanaburi province, western Thailand. The Khwae Noi merges with the Khwae Yai River to form the Mae Klong River and this species is possibly endemic to the latter drainage. There exist questionable records from the Bernam and Pahang rivers in northwestern and central Peninsular Malaysia, respectively.

Habitat

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

90 – 100 mm.

Aquarium SizeTop ↑

This species isn’t particularly active but a tank with base measurements of at least 90 cm x 30 cm is recommended since fluctuating water chemistry, typical of small aquaria, is unlikely to be tolerated long-term.

Maintenance

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

Diet

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.

Reproduction

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. septentrionalis differs from all other members by the following characters: shorter distance between dorsal and adipose fins (4.4-5.7% of standard length vs. 6.2-9.8%); fewer branchiostegal rays (4 vs. 5-6); body colouration almost uniformly cream with a few small, brown spots vs. variegated with many brown patches.

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.

References

1. de Pinna, M. C. C. 1996 - Fieldiana: Zoology (New Series) 84
   A Phylogenetic Analysis of the Asian Catfish Families Sisoridae, Akysidae, and Amblycipitidae, with a Hypothesis on the Relationships of the Neotropical Aspredinidae (Teleostei, Ostariophysi).
2. Ng, H. H. and H. H. Tan. 2002 - The Raffles Bulletin of Zoology 50(2): 449-452
   Redescription of Acrochordonichthys ischnosoma Bleeker, 1858, a poorly-known species of akysid catfish (Teleostei: Siluriformes) from Sumatra and Java.
3. Ng, H. H. and P. K. L. Ng. 2001 - Journal of Fish Biology 58(2): 386-418
   A revision of the akysid catfish genus Acrochordonichthys Bleeker.
4. Rainboth, W. J. 1996 - FAO, Rome, 265 p.
   Fishes of the Cambodian Mekong. FAO Species Identification Field Guide for Fishery Purposes.
5. Roberts, T.R. 1989 - Memoirs of the California Academy of Sciences 14: 210 p.
   The freshwater fishes of Western Borneo (Kalimantan Barat, Indonesia).
6. Sullivan, J. P., J. G. Lundberg and M. Hardman. 2006 - Molecular Phylogenetics and Evolution 41: 636–662
   A phylogenetic analysis of the major groups of catWshes (Teleostei: Siluriformes) using rag1 and rag2 nuclear gene sequences.
7. Vidthayanon, C. and H. H. Ng. 2003 - Zootaxa No. 183: 1-7
   Acrochordonichthys gyrinus, a new species of akysid catfish (Teleostei: Siluriformes) from Thailand.