Taxonomy & naming
Pangasius rheophilus was described by Bernard Pouyaud and Guy Teugels in 2000. It belongs to the family Pangasiidae, the shark catfishes, within the order Siluriformes, a group whose genus-level classification has been repeatedly revised over the last two centuries — many Pangasiidae were historically shuffled between broader catfish genera before the family was clarified. The species remains in Pangasius, and no reclassification is indicated by the available sources.
The genus name Pangasius derives from a local Southeast Asian vernacular name for these river catfishes. The specific epithet rheophilus is built from the Greek rheos ("stream, current, torrent") and philos ("loving") — "torrent-loving" — describing the species' preference for the fast, clear, running water of the upper Kayan River rather than the slow turbid stretches downstream.
Morphology
Pangasius rheophilus is a large, elongated shark catfish reaching a reported maximum of about 30.5 in standard length, among the bigger members of a genus that already contains some of the largest freshwater fishes in Southeast Asia. Like other Pangasius it has a streamlined, laterally compressed body, a forked tail, a tall sickle-shaped dorsal fin with a stiff leading spine, and long barbels used to feel out food in turbid water. Body width runs roughly 15–17% of standard length and the predorsal length about 35–36% of standard length, proportions consistent with an active, open-water swimmer.
As in all Pangasiidae, the skin is scaleless (naked), which has direct implications for medication sensitivity (see "In the aquarium"). The dorsal and pectoral fins carry stiff, locking spines typical of catfishes generally, useful for defence in the wild but a hazard to handle in captivity.
Habitat
This species is endemic to the Kayan River system in Bulungan, East Kalimantan, Indonesian Borneo — the type locality is Bulungan, Kalimantan Timur. It is not found in the Mekong or other mainland Southeast Asian rivers that host the more familiar farmed Pangasius species.
Immature fish range through the wider Kayan basin, including large pools near the sea with deep, turbid water. Mature fish, however, are apparently restricted to the upper reaches, where the river runs as clear, fast torrential water at an altitude of roughly 656–1312 ft — the rheophilic ("torrent-loving") habitat that gives the species its name. This upstream shift with maturity marks it as a river specialist tied to flowing, well-oxygenated water rather than still or sluggish habitats.
Feeding
Detailed dietary data specific to Pangasius rheophilus is sparse, but the genus is broadly omnivorous with a strong predatory streak as fish grow: general Pangasius biology includes detritus, plant matter and invertebrates, with juveniles taking zooplankton and small invertebrates and larger fish adding small fishes to the diet. Large adult Pangasius are capable of eating anything they can fit in their mouths.
In any setting large enough to house it, this species should be treated as a substantial predator: tankmates need to be too large to be swallowed, and large meaty foods — whole fish, prawn, and high-protein sinking pellets — suit its size and appetite far better than flake or small community foods.
Mating
There is no documented account of natural courtship or spawning behaviour for Pangasius rheophilus specifically. What is known from the genus more broadly is that large-bodied Pangasius species are riverine, migratory spawners in the wild, and that in captivity the group is reproduced almost exclusively through artificial, hormone-induced spawning at commercial aquaculture facilities rather than through natural pairing in a tank.
Given the species' huge adult size and its status as a narrow-range Kalimantan endemic rather than a farmed food fish, there is no record of home-aquarium spawning, and none should be expected.
Breeding
Pangasius rheophilus falls squarely into the large-commercial-catfish category: species in this genus that are bred at all are bred by hormone induction at fish-farm scale, not in home aquaria. Well-studied relatives such as P. hypophthalmus and P. bocourti have established, hormone-driven aquaculture breeding protocols, but P. rheophilus is a wild, geographically restricted torrent-dweller with no aquaculture or aquarium breeding record in the available sources.
In practice this species is simply not bred by hobbyists: it grows far too large for any home system, and reproducing it would require the induced-spawning infrastructure of a commercial hatchery. Anyone keeping this fish should treat it purely as a long-term, non-breeding specimen.
In the aquarium
Pangasius rheophilus is a textbook size-trap catfish. It is usually available, when available at all, as a small, silvery, active juvenile a few centimetres long — nothing about that juvenile hints at an adult that reaches roughly 30.5 in SL. No home aquarium can accommodate a fish of that eventual size; this is a public-aquarium or very large pond fish, not a tank fish, and it should not be bought on the strength of its juvenile appearance.
For keepers who do take on a young specimen with a genuine plan to rehome it before it outgrows captivity, note that the skin is scaleless, so medication — particularly copper-based treatments — should be dosed conservatively, as with loaches, puffers, and other naked-skinned catfish. The dorsal and pectoral spines lock rigid and can jab the keeper or snag a net; move the fish in a container rather than netting it. It is a strong, fast river swimmer that does best with powerful water movement and open swimming space, and as a predator its tankmates must be too large to be eaten. General Pangasius husbandry in culture uses warm water around 77–86 °F at a near-neutral pH of about 6.5–7.5, though the torrential upper-Kayan habitat of wild adults suggests this species in particular favours cooler, fast-flowing, well-oxygenated conditions rather than the warm still ponds used for the farmed Mekong species.
Conservation
The IUCN Red List assesses Pangasius rheophilus as Near Threatened. As a single-river endemic restricted to the Kayan system of East Kalimantan, with mature adults apparently confined to a narrow band of upper-river torrent habitat, the species has an inherently small range and is vulnerable to any disturbance of that habitat.
Pressures typical of Bornean river systems — logging, mining, damming, and general habitat degradation in Kalimantan — are the kind of threats likely to affect a narrow-range rheophilic fish like this one, though the cache sources reviewed here do not detail a specific threat assessment beyond the Near Threatened rating itself. This is not a farmed or widely traded aquaculture species, so trade pressure is not the primary conservation concern; habitat integrity in the Kayan basin is.