Kryptopterus macrocephalus

Kryptopterus: from the Greek kryptos, meaning 'hidden', and pterýgio, meaning 'fin', in reference to the reduced or absent dorsal-fin in members of this genus.

macrocephalus: from the Greek makros, meaning 'long', and kephalos, meaning 'head'.

Known from southern (peninsular) Thailand, Peninsular Malaysia, Singapore and the Greater Sunda Islands of Sumatra, Borneo and Java.

Type locality is usually given as 'Padang, Sumatra' although habitats in that area are said to be unsuitable for this species and it's never been recorded there post-description.

This species is a stenotypic inhabitant of peat swamp forests and associated blackwater streams.

Many such habitats have suffered large-scale degradation of some kind but in unaltered cases the dense canopy of branches above means very little light penetrates the surface of such environments, and riparian vegetation also tends to grow thickly.

Substrates are usually littered with fallen leaves, branches and submerged tree roots though in some places aquatic plants from genera such as Cryptocoryne or Barcalaya can be found.

The water is typically stained darkly with humic acids and other chemicals released by decaying organic materials, the dissolved mineral content generally negligible and pH as low as 3.0 or 4.0.

For example in Sarawak state, Malaysia (Borneo) it's been collected from a blackwater river known as the Sungai Kepayan which flows through remnant and intact peat swamp forest.

In 1998 pH was measured at 4.1 and depth ranged from 20 cm8 in to 2 metres or more.

Syntopic fish species included Osteochilus spilurus, 'Puntius' rhomboocellatus, Brevibora dorsiocellata, Trigonopoma gracile, T. pauciperforatum, Sundadanio cf. axelrodi, Kottelatlimia pristes, Neohomaloptera johorensis, Nanobagrus fuscus, Ompok weberi, Silurichthys phaiosoma, Hemirhamphodon phaiosoma, Betta edithae, B. midas, Nandus nebulosus, Belontia hasseltii, Luciocephalus pulcher, Parosphromenus anjunganensis, P. ornaticauda, and Sphaerichthys osphromenoides.

An aquarium with base dimensions of 120 ∗ 30 cm48 ∗ 12 in or equivalent should be the smallest considered.

Best kept in a well-decorated set-up with some surface or floating vegetation since it appears to prefer relatively dim conditions.

The addition of dried leaf litter and/or alder cones would further emphasise the natural feel while the tannins and other chemicals released by these as they decompose are considered beneficial for fishes from blackwater environments.

Do not add this fish to a biologically immature aquarium as it can be susceptible to swings in water chemistry.

Probably a predator feeding on crustaceans, invertebrates and smaller fishes in nature, although there should be no need to use such live foods in captivity.

Offer a varied diet comprising sinking dried foods, live and frozen bloodworm, Tubifex, etc., and perhaps the occasional small earthworm.

Generally peaceful though it may predate on smaller fishes and is somewhat timid so does not compete well with much larger, robust or otherwise boisterous species.

Peaceful, comparably-sized cyprinids, loaches and other catfishes perhaps constitute the best options but be sure to research your choices thoroughly prior to purchase.

K. macrocephalus is gregarious and tends to form schools so ideally four or more specimens should be purchased.

Adult males are noticeably slimmer than females and the posterior edge of the pectoral-fin spine is serrated (vs. smooth in females).

Unrecorded.

This species is also referred to as 'false glass catfish', 'mottled glass catfish' or 'tawny glass catfish'.

Roberts (1989) discusses the existence of striped and mottled colour forms but investigation is apparently required to establish whether these are conspecific or not.

The congener K. piperatus is very similar but has a colour pattern comprising a pale brown body with scattered dark spots vs. prominent dark brown spots or stripes in K. macrocephalus.

Kryptopterus species are found only in Southeast Asia and the genus has been considered polyphyletic since Bornbusch (1995) with some former species already moved to the genera Phalacronotus and Micronema.

Those still contained within the genus are assigned to a number of putative species groups as follows:

K. bicirrhis group: K. bicirrhis, K. lais, K. palembangensis, K. macrocephalus, K. minor, K. piperatus, K. vitreolus
K. cryptopterus group: K. cryptopterus, K. geminus
K. limpok group: K. limpok, K. mononema, K. dissitus, K. baramensis, K. hesperius
K. schilbeides group: K. schilbeides, K. paraschilbeides

Bombusch (1995) identified the K. bicirrhis group as a distinct clade although he didn't propose any synapomorphy to diagnose it.

Ng and Kottelat (2013)[6] later noted that members normally have fewer anal-fin rays (46–67 vs. 64–85) than other congeners and placed K. piperatus and K. vitreolus within the group based on this character.