Taxonomy & naming
Ompok ceylonensis was described by the German-British ichthyologist Albert Günther in 1864. It sits in the genus Ompok within the family Siluridae, the Old World sheatfishes that also contains the transparent glass catfishes (Kryptopterus) and the giant wallago (Wallago attu) of South and Southeast Asia. FishBase and the Catalog of Fishes both carry it under the genus Ompok, and that combination is used here.
Older literature on Siluridae has at times shuffled species among Ompok, Silurus and other historical genera as the family has been revised, and this species-group's boundaries have been reassessed in more recent taxonomic reviews of Ompok. No confirmed prior combination for this particular species turned up in available sources, so none is asserted here; Ompok ceylonensis is treated as the current, stable name.
Morphology
Like other silurids, Ompok ceylonensis has an elongated, laterally compressed body, a long-based anal fin, a small or absent dorsal fin, and a broad, flattened head with barbels used to feel out prey and obstacles in low light or turbid water. The skin is completely scaleless — smooth and naked, as in all members of the family.
FishBase records a maximum size of 11.5 in standard length for males and unsexed individuals. That is a substantial fish for a silurid catfish, and it is considerably larger than the small, silvery juveniles typically sold in the aquarium trade — a genuine size trap for buyers who see only the young fish in a shop tank.
Habitat
This species is endemic to Sri Lanka, where it inhabits freshwater river and stream systems as a demersal fish, holding near the bottom of clear, well-oxygenated, flowing water. FishBase classifies it as a freshwater demersal species restricted to the island.
As an island endemic with a naturally limited range, its populations are tied closely to the health of Sri Lanka's river systems; the species has no natural occurrence outside the country.
Feeding
Ompok ceylonensis carries a trophic level of roughly 3.9 on FishBase, placing it solidly among piscivorous predators. In the wild it is a nocturnal hunter, using its barbels to locate and ambush smaller fish and invertebrates it can swallow whole.
In the aquarium, juveniles typically start on live and frozen foods before graduating to flake and pellet foods, but adults revert to their natural piscivorous habits and will take any tankmate small enough to fit in their mouth. Any fish sharing a tank with an adult must be too large to be swallowed.
Mating
No documented spawning behaviour for Ompok ceylonensis was found in the sources consulted. Within Siluridae generally, the family spans very different reproductive strategies: the small glass catfishes (Kryptopterus) are essentially never bred in captivity and remain wild-caught in the trade, while larger river-dwelling sheatfish such as Ompok and Wallago species are typically river spawners whose captive supply, where it exists, comes from commercial fish-farm breeding rather than aquarium pairs courting and spawning at home.
Breeding
There is no established aquarium breeding record for Ompok ceylonensis in the sources available here, and none should be assumed. Larger Siluridae such as Ompok and Wallago are, where bred at all, generally propagated on fish farms using river-spawning conditions rather than in home tanks, and hobbyists should not expect to reproduce this species domestically. Anyone keeping this fish should treat it as a wild-origin or farm-origin animal rather than a captive-breeding project.
In the aquarium
This is a size-trap species: the small, attractive juveniles sold in shops grow into an adult approaching 11.5 in, and FishBase recommends a tank of at least 59 in in length to accommodate it — a footprint well beyond most standard home aquariums. Prospective keepers should plan for that adult size from the outset rather than being drawn in by a small starter fish.
Water should be clear, well-filtered and oxygen-rich, matching the flowing Sri Lankan streams this species comes from. Because it is completely scaleless, it is medication-sensitive: copper-based treatments and many standard medications should be dosed conservatively, often at half the labelled rate, as with other naked-skinned catfishes. It is a nocturnal predator, so daytime cover such as caves, overhangs or dense planting helps it settle, and tankmates must be robust and, critically, too large to be swallowed — this fish will eat any tankmate that fits in its mouth.
Conservation
The IUCN Red List assesses Ompok ceylonensis as Least Concern, an assessment dated 7 August 2019. FishBase lists its resilience as medium, with a minimum population doubling time of 1.4 to 4.4 years.
As a Sri Lankan endemic, its long-term outlook is tied to the condition of the island's river systems rather than to any single, well-documented threat; no species-specific conservation programme was found in the sources consulted.