Taxonomy & naming
Ompok bimaculatus was first described by the German naturalist Marcus Elieser Bloch in 1794, who originally placed it in the genus Silurus — giving the old combination Silurus bimaculatus, which appears frequently in older literature. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Ompok bimaculatus as the current valid name, with Bloch credited as the original describer.
The genus Ompok belongs to the family Siluridae, the sheatfishes, a group of scaleless, elongate catfishes distributed across Asia and into Europe. Siluridae encompasses some of the largest freshwater catfishes in the world, and Ompok, while smaller than the giant Wallago or Silurus, still encompasses species that substantially outgrow the space most hobbyists can provide. The epithet bimaculatus is Latin for 'two-spotted', referring to the pair of dark shoulder spots that are a useful identification mark on juveniles.
Morphology
Ompok bimaculatus has the flattened, elongate build typical of the silurids: a broad, depressed head, a wide mouth set at the front of the snout, a long and laterally compressed body, and a long, low anal fin that runs almost to the tail — a distinctive family trait. Two pairs of barbels are present: the maxillary pair (upper jaw) is long and reaches past the pectoral base, while the mandibular pair is shorter. The dorsal fin is small and placed well forward.
The body is naked — entirely scaleless — and in juveniles the flanks can show a ghostly translucency, explaining the common name glass catfish for some members of the group. A pair of conspicuous dark blotches sits on the shoulder just behind the head on juveniles; these may fade with age in larger adults. Maximum size is reported as 19.5 in standard length (FishBase), with some records citing up to 23.5 in total length. Pectoral and dorsal fins carry stiff, locking spines that can tangle in a net and jab the keeper.
Habitat
Ompok bimaculatus occupies a wide variety of lowland freshwater environments across South and Southeast Asia, including slow-moving rivers, floodplain oxbow lakes, swamps, ponds and irrigation canals. Its native range spans India, Myanmar, Thailand and Laos, and it is one of the more widespread members of its genus. It tolerates a range of conditions but is primarily a fish of warm, productive lowland waters.
Water conditions in its native range are generally warm — around 75–84 °F — and while specific pH data vary across its broad range, these are typically soft to moderately hard, near-neutral to slightly acidic river systems rather than extreme blackwater or alkaline rift-lake conditions. The species is essentially a floodplain generalist, exploiting the seasonal connectivity between rivers and peripheral wetlands.
Feeding
Ompok bimaculatus is a piscivore and opportunistic predator. Juveniles take small invertebrates — insects, crustaceans and worms — but as the fish grows it shifts increasingly to fish prey, and adults will take any fish or invertebrate they can swallow whole. In the wild this means small schooling fish sharing the same floodplain waters; in the aquarium it means any tankmate that fits in the mouth is at risk.
In captivity, established adults accept large meaty foods: whole prawns, strips of fish, large pellets and other sinking prepared foods. Live or frozen fish are readily taken. Feeding primarily occurs after dark; this species is strongly nocturnal and is rarely active under bright lights. Tankmates must be significantly larger than the catfish's gape to be safe — a rule that becomes progressively harder to satisfy as the fish grows toward 19.5 in.
Mating
Mating behaviour in Ompok bimaculatus has not been documented in detail for the aquarium hobby, and the species is not bred with any regularity in captivity. In the wild, like other large silurids, it is presumed to spawn seasonally in association with the annual monsoon flood pulse, which triggers migration and reproductive activity across many South Asian riverine catfishes.
Large silurid catfishes in this genus are believed to scatter eggs over submerged vegetation or substrate in flooded marginal areas without elaborate parental care, but captive accounts are essentially absent. Sexing live individuals in aquaria is not straightforward; females may be fuller-bodied when gravid, but this is not a reliable or well-documented field mark in the literature available.
Breeding
Ompok bimaculatus is not bred in home aquaria. Commercial supply of the species — where it appears in trade at all — relies on wild collection or, in parts of its range, aquaculture production involving hormonal induction, as is common for large Asian catfishes grown for food. The species is a food fish of economic importance in parts of India and Southeast Asia, and farmed production is geared toward the food trade rather than the ornamental market.
Hobbyist breeding is not established and should not be expected. The size alone — a specimen approaching 19.5 in or larger — makes most domestic setups impractical as breeding quarters. Keepers who acquire this species should plan for its full adult size and not anticipate captive reproduction.
In the aquarium
Ompok bimaculatus is a species for experienced keepers with very large systems — the adult size of up to 19.5–23.5 in total length demands a tank of at minimum 105–130 US gal for a single specimen, and a public-aquarium or indoor pond setting is more realistic. This point cannot be overstated: the species is frequently sold as a small, appealing juvenile and grows into a fish that most hobbyists cannot ethically house. Prospective buyers should plan for the adult size before purchase.
As a scaleless silurid, Ompok bimaculatus is sensitive to copper and to many standard aquarium medications. Treatments should be used at reduced doses — typically half the normal dose or less — and the fish monitored closely during any treatment course. The same caution applies to salt, organophosphate-based remedies and some antiparasitic agents. Move this fish in a container, never a net: the locking pectoral and dorsal spines will tangle in mesh and can inflict a painful jab.
Care requirements are otherwise straightforward for the size: warm, clean water in the 75–84 °F range, moderate to subdued lighting, heavy planting or other cover for daytime retreats, and a secure lid (silurids are capable escape artists). Tankmates must be considerably larger than the catfish's mouth; any fish small enough to swallow will be eaten. Feeding after lights-out, when the fish is naturally active, gives the best results.
Conservation
The IUCN Red List assessed Ompok bimaculatus as Least Concern in 2011. The species is broadly distributed across South and Southeast Asia and is not currently considered threatened at the range-wide level. Its population trend was assessed as stable, reflecting its adaptability to a range of freshwater habitats including rivers, lakes and swamps.
Locally, pressures include habitat degradation, floodplain modification and overfishing, as the species is valued as a food fish in parts of India, Myanmar and Thailand. Intensification of agriculture and associated water abstraction and pollution in lowland river systems across its range represent the most relevant ongoing threats, though none are currently sufficient to trigger a threatened listing. The ornamental trade in this species is limited and is not considered a significant conservation concern.