The genus is recognized to be paraphyletic. The species of Ompok have been grouped into species groups, such as the Ompok bimaculatus group (ie. O. bimaculatus, O. malabaricus, O. miostomus), the O. eugeneiatus group (ie. O. eugeneiatus, O. pinnatus), the O. hypophthalmus group (ie. O. hypopthalmus, O. rhabdinurus, O. urbaini), and the  O. leiacanthus group (O. fumidus, O. jaynei, O. leiacanthus). On the other hand, the monophyly of these species groups is not strong enough to reassign species to other genera. The O. eugeneiatus group is likely to be more closely related to Kryptopterus than the other Ompok species. According to the recent catfish checklist, O.eugeneiatus has been reclassified into Kryptopterus, however O. pinnatus has not. Dorsal soft rays (total): 4 - 4; Anal soft rays: 54 – 74. Two pairs of barbels; maxillary barbels reaching pelvic fins or anal fins; mandibulary barbels minute, about as long as diameter of eye. Eyes small, covered by skin. Dorsal and pelvic fins small; anal fin long; pectoral fins well developed; vomerine teeth in 2 patches.. Colour: Brown, usually  marmorated body with conspicuous round black blotch above pectoral base. Habitat: Occurs in streams and rivers of all sizes with currents ranging from sluggish to moderate. Found in quiet, shallow (0.5-1.5 m), often muddy water, in sandy streams, rivers and  tanks. Also occurs in canals, beels and inundated fields. Moves into freshly inundated habitats during the flood season. Feeds on vegetable matter, fish, crustaceans and mollusks. Sold fresh or smoked on skewers. Remarks: The catfish genus Ompok La  Cepède, 1803, consists of medium-sized silurid fishes found in inland waters throughout  South and Southeast Asia. The genus is traditionally diagnosed by the presence of a short dorsal fin with 4 rays, strongly forked caudal fin, subcutaneous eye that is set immediately posterior to the mouth rictus and two patches of palatal teeth (Weber & de Beaufort, 1913). Bornbusch (1995) showed that Ompok, as currently understood, is probably paraphyletic. However, given the weak support for the monophyly of his clades and the difficulty in identifying synapomorphies to easily diagnose genera, there has been little change in the taxonomy of this group. The specimens from Malaysia may be another species, namely O.siluroides, which is currently a synonym of O.bimaculatus.