Taxonomy & naming
Ompok pinnatus was described by the Singaporean ichthyologist Heok Hee Ng in 2003. It belongs to the family Siluridae — the Old World glass and sheatfish catfishes — and to the genus Ompok, a group of scaleless Asian catfishes that ranges from small, slender "glass catfish" types to much larger river sheatfish. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Ompok pinnatus as a valid species and the current, correct combination; it has not been shuffled through other genera in the way many older Siluriformes names have been.
The genus name Ompok is a vernacular Malay/Sundanese term for these catfishes, adopted into scientific use. The species epithet pinnatus is Latin for "feathered" or "winged", almost certainly referring to the fish's long, trailing fin rays and barbels. In the trade it circulates under the common names "longfin glass catfish" and, in the German aquarium literature, "Ruebezahl glass catfish".
Morphology
Like other Siluridae, Ompok pinnatus has a laterally compressed, knife-shaped body, a long-based anal fin, and no dorsal fin spine — the small dorsal fin sits far forward. The skin is completely scaleless and semi-translucent, giving the fish the pale, glassy look shared by its relatives. Its most distinctive feature is a pair of extremely long, thread-like maxillary barbels that can trail well past the body, used to feel out food and surroundings in low light or turbid water.
Maximum reported length is only about 3–4 in total length, making this a genuinely small catfish rather than one that outgrows its keeper's expectations. The species shows a modest sexual dimorphism: males carry a serrated pectoral fin spine, while the pectoral spine in females and juveniles is smooth-edged, a feature useful for sexing adult fish.
Habitat
Ompok pinnatus is native to Southeast Asia, where it inhabits slow-flowing rivers, streams and floodplain waters typical of the region's lowland freshwater and brackish-influenced systems. Precise distribution data is sparse for this species — it is one of the more recently described and less-studied members of a large genus — but it shares the general lowland Siluridae habitat of quiet, vegetated or leaf-littered water with modest current.
Reported aquarium water parameters place it in warm, near-neutral water: roughly 75–81 °F with a pH around 6.8–7.4. This fits the pattern of many Southeast Asian lowland catfishes, though as with much of its natural history, detailed field data on the wild population is limited.
Feeding
Ompok pinnatus is carnivorous, feeding on small crustaceans, aquatic insects and other invertebrates in the wild. Its long barbels help it locate prey by touch, an adaptation suited to its typically low-light, crepuscular or nocturnal foraging habits.
In the aquarium it accepts frozen and prepared carnivore foods readily — bloodworm, brine shrimp, chopped prawn and sinking pellets are all taken. Because it is genuinely small, its dietary needs scale accordingly: very small fish or fry sharing the tank risk being eaten, but tankmates of ordinary community size are in no danger from a fish this size.
Mating
No courtship or spawning behaviour has been documented for Ompok pinnatus specifically. Glass catfishes in general (the genus Kryptopterus) are essentially never bred in the home aquarium and the trade in those species is wild-caught; larger river-dwelling Ompok and the related genus Wallago are river spawners whose reproduction is tied to seasonal flooding and is mostly replicated only at commercial fish-farm scale, using hormone induction rather than natural pairing.
Given the sparse data on this particular species, it is honest to say that its mating behaviour in the wild has not been described in the literature available, and nothing suggests it departs from the broader Siluridae pattern of river-linked, seasonal spawning rather than any home-tank-observable courtship.
Breeding
Home aquarium breeding of Ompok pinnatus is not established. As with most small Siluridae glass catfishes, the aquarium supply is believed to be wild-caught or, at most, produced at commercial scale using hormone-induced spawning of the kind used for larger farmed Ompok and Wallago species — not a technique replicable in a home tank. No parental care has been reported, consistent with the open-water, unguarded spawning typical of river sheatfish.
Prospective keepers should not expect to breed this species and should treat wild or farm-collected stock as the only realistic aquarium source at present.
In the aquarium
Ompok pinnatus is a genuinely small, peaceful catfish — a refreshing exception among Ompok, several of which are size-trap species sold small and grown into pond-sized fish. At only 3–4 in, it stays manageable in a modest aquarium, and its calm, loosely schooling temperament makes it a good community fish for tankmates too large to be swallowed. Keep it in a small group rather than alone; it is a sociable species that does poorly in isolation.
Two care points follow directly from its biology. First, like all Siluridae it is completely scaleless, so it is more sensitive than scaled fish to copper and many medications — dose conservatively, as with loaches and other naked-skinned catfishes. Second, males carry a serrated pectoral spine that can catch in a net, so it is worth scooping the fish gently or using a container rather than forcing it through fine netting. Provide dim lighting, plant cover or floating vegetation, and gentle flow to mimic its lowland river habitat, and feed after lights-dim given its crepuscular foraging habits.
Conservation
The IUCN Red List assesses Ompok pinnatus as Data Deficient, last evaluated in 2011. This reflects how little is documented about the species' population size, trend and precise range rather than any confirmed stability or decline — it is one of many small, recently described Southeast Asian catfishes that has not received a full population assessment.
As with other Data Deficient Siluriformes, the responsible approach is caution: avoid assuming the wild population is secure, support sustainably sourced stock where traceable, and recognise that lowland Southeast Asian freshwater habitats broadly face pressure from damming, drainage and water quality decline, any of which could affect a species this poorly surveyed.