Taxonomy & naming
Ompok fumidus was described by Heok Hee Tan and Peter Ng in 1996, one of several species split out of the wide-ranging Ompok leiacanthus complex once that group was revised. It sits in the family Siluridae, the Old World sheatfishes and glass catfishes, alongside relatives such as Kryptopterus, Wallago and Silurus. The Catalog of Fishes treats Ompok fumidus as the valid name; older literature and some trade lists still lump material of this species under the broader O. leiacanthus, so specimens sold or catalogued that way may in fact belong here.
FishBase groups O. fumidus together with O. jaynei and O. leiacanthus as the closest members of the leiacanthus species group, distinguished mainly on fin-ray counts and other fine anatomical detail rather than anything obvious to the aquarist. As with much of Siluriformes, the genus-level arrangement of Ompok has been repeatedly revised, so the name attached to imported fish should be treated with some caution.
Morphology
Like other Ompok, O. fumidus has the classic sheatfish silhouette: a laterally compressed, elongated body, a long-based anal fin (roughly 53–60 soft rays) running most of the length of the underside, a short dorsal fin set well forward, and a small adipose fin. The skin is entirely scaleless, smooth and often faintly translucent, in keeping with the family's glass-catfish relatives, and colouration is generally a subdued silvery-grey to smoky brown, muted rather than showy.
Published maximum size is 6 in standard length (FishBase), making this one of the smaller Ompok species — genuinely modest by the standards of a genus whose larger members are sold as juveniles and grow well beyond typical home-aquarium size. Even so, buyers should not assume every Ompok on offer stays this small; verify the actual species before committing to a small tank, since aquarium-trade specimens are frequently mislabelled within this species group.
Habitat
Ompok fumidus is known from Peninsular Malaysia (Terengganu, Selangor, Perak, Pahang) and from Indonesia, including Pulau Bintan in the Riau Archipelago and the Kalimantan Barat and Kalimantan Tengah provinces of Indonesian Borneo. It is a peat-swamp specialist, taken from shallow, blackwater habitats — the tannin-stained, acidic waters draining lowland peat forest — and appears to be stenotopic, meaning it is tied fairly narrowly to that specific habitat type rather than tolerating a broad range of conditions.
This is a fragile habitat under real pressure: peat-swamp forest across Sundaland has been extensively logged and converted, and FishBase specifically notes that populations of this species occur in areas heavily disturbed by logging. Aquarium water should therefore lean toward the soft, acidic, tannin-rich conditions of a peat swamp rather than the harder, more neutral water typical of many other Southeast Asian rivers.
Feeding
Diet shifts with age. FishBase reports that O. fumidus feeds mainly on insect larvae, but that adults turn increasingly to fish. In practice this makes it an opportunistic small predator: a fish that will take any prey item — invertebrate or fish — small enough to swallow, in the manner typical of sheatfish catfishes generally.
In the aquarium this translates into a preference for meaty foods: frozen bloodworm and other insect-larva analogues, small feeder-safe live or frozen fish, prawn, and sinking carnivore pellets once the fish is settled onto prepared foods. Tankmates should always be sized with this predatory streak in mind — anything small enough to fit in the mouth is at risk, and no amount of gentle temperament in the aquarium literature should be read as vegetarian intent.
Mating
No published account describes courtship or spawning behaviour for Ompok fumidus specifically, and the species does not appear to have an established aquarium-breeding history. Among the sheatfish catfishes generally, the true glass catfishes (Kryptopterus) are essentially never bred in captivity, and the larger river-dwelling Ompok, Wallago and Silurus species that have been propagated are mostly produced through farm-scale, often hormone-assisted spawning rather than natural pairing in a home tank.
Given the lack of species-specific data, the safest assumption is that O. fumidus follows the pattern of its larger relatives — a river or blackwater spawner with no documented parental care — but this should be treated as inference from the wider genus rather than a confirmed account for this species.
Breeding
There is no confirmed record of Ompok fumidus being bred in home aquaria, and the cache of available sources gives no breeding details to report. This mirrors the broader pattern in Siluridae: small glass catfishes are essentially unbred in captivity and the trade in them is wild-caught, while the larger sheatfishes that reach commercial production do so at fish-farm scale with hormone induction, not through hobbyist spawning.
Hobbyists should assume any specimens in the trade are wild-collected from Malaysian or Indonesian peat swamps rather than captive-bred, and treat claims of home breeding for this species with scepticism until better documented.
In the aquarium
At a modest maximum of about 6 in standard length, O. fumidus is one of the more manageable Ompok for a dedicated setup, but it still wants a reasonably long, well-covered tank with strong water movement — Aquarium Glaser notes that Ompok cats from these blackwater brooks are used to roughly a 10x-per-hour turnover and do best with vigorous, clean-water circulation even though they don't seem to mind the current itself. Water should be soft and on the acidic side, echoing its peat-swamp origin, and lightly tannin-stained water (via driftwood or blackwater extract) is a reasonable approximation of habitat. It is reported as a jumper when startled, so a tight-fitting, well-sealed lid is essential.
Two care points follow directly from its biology as a catfish. First, its skin is entirely scaleless, so it is more sensitive than scaled fish to copper-based medications and many standard treatments — dose conservatively, often at half strength, and remove the fish from copper-treated water where possible. Second, it is mostly a dusk-and-night forager, so it appreciates driftwood, roots or dim cover to retreat into by day; keep small tankmates only if you are prepared for some of them to disappear, since this species will take any fish it can fit in its mouth. Some sources note captive individuals reaching closer to 8 in, so plan tank size around the larger end of the range rather than the FishBase minimum.
Conservation
The IUCN Red List assesses Ompok fumidus as Near Threatened, reflecting genuine concern about the state of its peat-swamp habitat across Peninsular Malaysia and Indonesian Borneo. Lowland peat-swamp forest in this part of Sundaland has been extensively logged, drained and converted to agriculture, and FishBase notes explicitly that this species occurs in areas heavily disturbed by logging — exactly the kind of habitat degradation that erodes stenotopic, specialist species faster than generalists.
Because no captive-breeding programme is documented for this species, any ongoing aquarium trade almost certainly draws on wild populations, adding collection pressure on top of habitat loss. Buyers who want to support the species' wild population might reasonably favour captive-bred alternatives within the family where available, and treat wild-collected O. fumidus as a fish that comes from an already-stressed habitat.