Taxonomy & naming
Belodontichthys dinema was described by the Dutch ichthyologist Pieter Bleeker in 1851 from Bandjarmasin (Banjarmasin), Borneo, Indonesia. It belongs to the family Siluridae, the Old World sheatfishes and glass catfishes, a family whose other well-known members include the true glass catfish genus Kryptopterus, the walking-catfish-shaped Wallago, and the European wels catfish Silurus glanis. The Catalog of Fishes treats Belodontichthys dinema as the valid name in the monotypic-leaning genus Belodontichthys, which holds only a small number of species distinguished by their long, sabre-like jaw teeth.
The genus name Belodontichthys is built from Greek belone (dart, needle) and odous (tooth) plus ichthys (fish) — "needle-toothed fish" — a direct reference to the long, fang-like teeth used to seize fast-moving prey. Historically this species and its relatives have circulated under various older Siluridae combinations in the aquarium trade and older literature; the Catalog of Fishes' current placement in Belodontichthys is followed here. Reports of this species from the Mekong basin are now considered misidentifications of the closely related Belodontichthys truncatus, so aquarium stock labelled "dinema" from Mekong sources should be treated with caution.
Morphology
Belodontichthys dinema has the classic silurid "sheatfish" silhouette: a long, laterally compressed, knife-like body, a low sloping head, a large upward-angled mouth, and an extremely long anal fin that runs nearly the length of the body and fuses visually with a small, deeply forked caudal fin. The dorsal fin is reduced to a tiny vestige or is essentially absent, typical of the family. Two pairs of long, whip-like barbels frame the jaw.
The body is a translucent silver to olive-grey, often with a faint iridescent sheen, countershaded for a mid-water ambush predator. The mouth is armed with numerous long, sharp, needle-like teeth — the feature the genus is named for — built for gripping and swallowing slippery fish prey rather than crushing. Like other Siluridae it is scaleless, naked-skinned, which makes it more sensitive than scaled fish to copper-based medications and to many standard treatments; dose conservatively. FishBase records a maximum size of 39.5 in total length — a genuinely large predatory catfish, not a small or medium aquarium species, and the size trap is real: juveniles sold at a modest size can outgrow all but the largest home aquaria.
Habitat
The species is native to Southeast Asia — the Malay Peninsula, Sumatra and Borneo — where it inhabits medium to large lowland rivers, holding station at middle depths and near the surface in the deeper reaches of these systems. It is a freshwater, demersal-to-midwater, potamodromous fish, meaning it makes freshwater migrations within river systems rather than needing to reach the sea.
Water in its native rivers is generally soft to moderately hard and close to neutral; aquarium-trade guidance places it around pH 6.8–7.8, at warm tropical temperatures of roughly 75–82 °F, in clean, well-oxygenated water with moderate current — a fast-flowing to slow-flowing lowland river fish rather than a still-water species. It prefers water with some movement, reflecting its habit of holding position and striking at passing prey in current.
Feeding
Belodontichthys dinema is a strict, nocturnal piscivore — an obligate fish-eater, not a generalist omnivore. In the wild it hunts small to medium fish, striking from ambush with its needle-toothed jaws, and is most active after dark. It largely ignores frogs and large shrimp, and generally needs to see prey moving to trigger a feeding strike, a trait that makes weaning some individuals onto prepared foods difficult.
In the aquarium some specimens can be trained onto frozen whole fish or large frozen prey items, but others will accept only live or freshly killed fish, and keepers should be prepared for a genuinely carnivorous, fish-only diet — this is not a species to keep with anything small enough to be viewed as food. Feeding after lights-out, matching its nocturnal habits, gets the best results and avoids stressing a fish that hunts primarily by ambush in low light.
Mating
Specific documentation of courtship and spawning behaviour in Belodontichthys dinema is sparse. As a large, migratory river Siluridae species it is presumed to follow the broad pattern of many potamodromous riverine catfishes — seasonal movement associated with rising water and open, unguarded egg release rather than nest-building — but no detailed wild spawning account for this species is confirmed here, and nothing should be inferred beyond that generality.
Breeding
Belodontichthys dinema has not been successfully bred in captivity, and its wild breeding biology remains essentially undocumented. This places it with the large-river Siluridae and other big, obligately predatory catfishes that are simply not achievable home-aquarium breeding projects: any specimens in the trade are wild-collected or, where large-scale culture exists for similar Southeast Asian river species, produced by hormone-induced commercial spawning rather than by hobbyists. Aquarists should not expect to breed this species and should treat any claim of home spawning with scepticism absent documentation.
In the aquarium
This is a large-tank, experienced-keeper-only fish, and the size trap is the single most important care point: FishBase gives a maximum of 39.5 in total length, the trade regularly moves specimens already 40+ cm, and aquarium guidance calls for a minimum of roughly 200 gallons (750+ litres) even for a sub-adult, with more needed as the fish approaches full size. Buying a small juvenile without planning for a fish approaching a metre long is the classic mistake with this species.
Water should be kept clean and well-oxygenated, pH roughly 6.8–7.8, temperature about 75–82 °F, with moderate current and stable, low-nitrate conditions — it is reported as hardy once established in good water, but intolerant of poor water quality. Because it is scaleless it is medication-sensitive; use copper and other treatments conservatively, at reduced dosing, as with loaches, puffers and other naked-skinned catfishes. It is strictly predatory, so tankmates must be too large to be eaten — this rules out community fish entirely and calls for other large, robust river species. Provide open swimming space in mid-water rather than dense cover, since it is not a bottom-hugging cave dweller like many catfishes, and dim lighting or shaded refuge helps this nocturnal hunter settle. As with other large Siluridae, handle only with a container rather than a net when moving it, since a thrashing fish this size and shape is easily injured or can injure the keeper.
Conservation
The IUCN Red List assesses Belodontichthys dinema as Least Concern, reflecting its relatively wide distribution across river systems of the Malay Peninsula, Sumatra and Borneo. It faces the general pressures common to Southeast Asian lowland rivers — habitat degradation, damming and water-quality decline — but is not currently considered at elevated extinction risk. As with many large Southeast Asian river catfishes, aquarium-trade specimens are believed to be wild-collected rather than commercially farmed, so responsible sourcing and awareness of its eventual adult size matter for both the fish and the wild population it comes from.