In a recent issue of the Journal of Fish Biology, Ng Heok Hee and Peter Ng completed a revision of the genus Silurichthys of the family Siluridae. Among the authors' findings were the fact that all members of the genus appear to exhibit sexual dimorphism. Mature males have thickened pectoral spines with three to eight distinct posterior serrae. To the naked eye these serrae look like small teeth on the pectoral spine. The authors' also note that they have found this type of sexual dimorpism in the silurid genera Ompok, Pterocryptis, and Hemisilurus.
Silurichthys indragiriensis
The genus Silurichthys now contains the following species:
Silurichthys citatus Ng & Kottelat, 1997: Known from the Kapaus basin in western Borneo. Caught only in streams with clear, swift water. Most of the fish species found with S. citatus are specialized for living in fast-flowing water, such as Glyptothorax and Gastromyzon.
Silurichthys gibbiceps Ng & Ng, 1998: Known from the Barito basin in southern Borneo. The type series was collected from a shaded stream running through abandoned fields. The stream had small pools, sandy runs, and many fallen tree limbs. The fish were captured near the fallen limbs.
Silurichthys hasseltii Bleeker, 1858: Known from western Java, Bangka, Bintan, Batam, Singapore, and southern Peninsular Malaysia. These fish are primarily found in acid water swamps and forest streams. They spend the day hidden beneath submerged logs and leaf litter and come out at night to feed at the surface on insects.
Silurichthys indragiriensis Volz, 1904: Known from central Sumatra, Bintan, Bangka, Billiton, and Peninsular Malaysia. This fish is usually found in blackwater habitats associated with peat swamps. Most of the fish the authors obtained were from acidic (pH 4-5) tannin-stained waters. The fish hides in the leaf litter during the day.
Silurichthys marmoratus Ng & Ng, 1998: Known only from northern and western Borneo. Found in both acid water forest streams and blackwater habitats in peat swamps.
Silurichthys phaiosoma (Bleeker, 1851): Known from northwestern Borneo where it is found in acidic blackwater peat swamps (pH 4-5).
Silurichthys sanguineus Roberts, 1989: Known only from the Kapaus basin in western Borneo. The holotype was collected in a small forest stream (pH 6.5 temp. 25°C)
Silurichthys schneideri Volz, 1904: Known from northern Sumatra, northern Peninsular Malaysia, southern and southeastern Thailand, and southern Cambodia. The fish is found in fast-flowing mountain streams with a sandy or rocky substrate and can be found hiding under rocks. The pH averages 6-7.
Reference: Ng H. H. & P. K. L. Ng. 1998. A revision of the South-east Asian catfish genus Silurichthys. Journal of Fish Biology 52: 291-333.