Taxonomy & naming
Pangasius larnaudii was described by the French zoologist Marie-Firmin Bocourt in 1866. It belongs to the family Pangasiidae, the shark catfishes of South and Southeast Asia, and to the nominal genus Pangasius, which the Catalog of Fishes (Eschmeyer, CAS) treats as the valid placement. Pangasiidae are placed within the order Siluriformes.
The family Pangasiidae includes some of the largest freshwater fish in the world, including the giant Mekong catfish Pangasianodon gigas. Pangasius larnaudii is sometimes confused in the trade with Pangasianodon hypophthalmus (the iridescent shark proper), which is the species most commonly seen in mass aquarium retail; the two are related but distinct species, both prone to the same size-trap problem. Historical synonymy in this group is complex, and older references may place Asian shark catfishes under Silurus or related genera.
Morphology
Pangasius larnaudii has the long, laterally compressed, torpedo-shaped body characteristic of the family. The dorsal surface is dark grey to charcoal, fading to silver on the flanks, with a pale or cream-white belly. The tail is deeply forked. Two pairs of short barbels are present on the upper and lower jaw. The skin is completely scaleless and smooth — there is no bony armour as in loricariids — which makes this species particularly vulnerable to copper and other medications that accumulate through the skin.
FishBase records maximum standard length at around 47–51 in in the wild, making this one of the larger Pangasius. Juveniles show the iridescent silver sheen that gives the group its common name; this fades with age. Like other pangasiids, the species has a stiff, locking dorsal spine, and the pectoral spines are serrated and can lock erect — a handling hazard that is best managed by transferring the fish in a container rather than netting it.
Habitat
The species is native to the Mekong River basin, including lowland reaches in Thailand, Cambodia and Laos. It occupies large river channels and their floodplain extensions, favouring deeper, open-water stretches rather than thickly vegetated margins. Like most large Mekong catfishes it makes seasonal migrations tied to the monsoon flood pulse, moving between feeding and spawning grounds.
Mekong water in the lowland reaches is warm — typically 75–82 °F — and circumneutral to slightly acidic, with moderate dissolved solids. These are not blackwater conditions; the large tropical river delivers well-oxygenated, moderately mineralised water. Turbid conditions are common during flood season.
Feeding
Pangasius larnaudii is a piscivore and generalist predator. In the wild it hunts other fish, invertebrates and whatever organic matter the river's flood pulse makes available, feeding predominantly after dark. Its large gape means any tankmate it can physically swallow is at risk.
In captivity it accepts large meaty foods readily: pieces of fish, prawns, earthworms, and large sinking carnivore pellets. Feeding should take place in low light or after lights-out to match its nocturnal habits. Tankmates must be substantially larger than the catfish's gape; any small fish — including juveniles of otherwise robust species — will be predated.
Mating
Mating in Pangasius larnaudii, as in other large pangasiids, occurs in the wild during seasonal spawning migrations tied to the Mekong's monsoon flood cycle. Ripe adults aggregate and broadcast spawn in open water, with fertilisation external. The environmental triggers — temperature shift, rising water level and barometric change — are not reproducible in a home aquarium.
In commercial aquaculture, spawning is induced with hormonal injections (typically carp pituitary extract or HCG); natural pairing in captivity without hormone treatment is not reported. Reliable differentiation of the sexes is not documented for home-aquarium purposes.
Breeding
Pangasius larnaudii is not bred in home aquaria. The combination of enormous adult size (making even a species-only tank impractical for most keepers), the need for seasonal environmental triggers, and the reliance on hormone-induced spawning places successful reproduction firmly in the domain of commercial fish farms and university aquaculture facilities.
Virtually all specimens sold in the aquarium trade are farm-bred juveniles, produced through hormone-induced spawning in Southeast Asian aquaculture operations. This is the norm across large pangasiids. Keepers should not expect to breed this fish and should plan for long-term housing as a non-reproductive display animal.
In the aquarium
Pangasius larnaudii is one of the clearest examples of the size-trap problem in the aquarium trade. Juveniles of 2–4 in are commonly sold, grow rapidly under good conditions, and quickly outpace any reasonable home aquarium. Wild adults reach 47–51 in; aquarium specimens often reach 8–12 in before owners realise the trajectory, but growth continues well beyond that. Housing a large adult requires an indoor or outdoor pond or a public-aquarium-scale installation. The species should not be purchased for a home aquarium unless facilities for very large fish are already in place.
Two care considerations are non-negotiable regardless of tank size. First, the scaleless skin makes this species highly sensitive to copper-based medications and many anti-parasitic treatments — doses that a scaled fish tolerates may be lethal here. If treatment is necessary, use a half dose, observe closely, and prefer medications formulated for scaleless fish. Second, the locking pectoral and dorsal spines tangle fatally in nets — always transfer this fish in a container (a large bucket or bowl) and never net it. Standard maintenance water temperature is 75–82 °F at circumneutral pH. The fish is nocturnal and benefits from subdued lighting and open swimming space, though it rarely hides. It is not aggressive toward fish it cannot swallow but will consume anything small enough to fit in its mouth.
Conservation
The IUCN Red List now assesses Pangasius larnaudii as Least Concern. The Mekong basin nonetheless faces substantial pressure: hydroelectric dam construction on both the mainstream and tributaries interrupts the seasonal migrations on which large catfishes depend for spawning; floodplain conversion reduces rearing habitat; and commercial fisheries take large pangasiids directly for food. The species is also collected (as juveniles) for the aquarium trade, though that pressure is minor relative to direct harvest.
Conservation of this species remains tied to the health of the large-river flood-pulse system and to mitigation of dam impacts across the Mekong drainage, even under the current Least Concern rating.