Pangasius macronema is a slender freshwater catfish native to parts of Southeast Asia, yet it has become largely unknown even in its own region. Known in Indonesia by local names such as lancang or rius, this modest member of the Pangasiidae family bears distinctive long barbels (whiskers) that extend well past the length of its head. It inhabits rivers from Java and southern Borneo to the great Mekong and Chao Phraya basins of Indochina. Once a humble staple of regional fisheries, the lancang has quietly slipped from popular attention over recent decades.

In the wild, P. macronema typically forms large schools in the main channels of big rivers. It is relatively small (maxing out around 30 cm in length) with an elongated, deep-bodied form and smooth scaleless skin. FishBase notes it lacks the dark lateral stripe common in some catfish, but is distinguished by a maxillary barbel that reaches the base of the pectoral fin. During the rainy season the lancang often moves into flooded tributaries and forested backwaters, foraging on mollusks, insects and small fish as waters rise. Although little-studied, it is still harvested locally – in fact, FishBase reports it is marketed fresh in local fish markets much like other pangasius catfish.

Taxonomy and morphology

Among the vast diversity of freshwater species inhabiting Southeast Asian river, Pangasius macronema stands out as a notable member of the catfish order. Belonging to the group commonly referred to as whiskered catfish—scientifically classified under the order Siluriformes—this species is a part of the family Pangasidae, a lineage known for its economic and ecological importance across the region.

Here is the species’ scientific classification:

• Kingdom: Animalia
• Phylum: Chordata
• Class: Osteichthyes (bony fishes)
• Order: Siluriformes (catfish)
• Family: Pangasidae
• Genus: Pangasius
• Species: Pangasius macronema

P. macronema is relatively small for a catfish, rarely exceeding about 20–25 cm in total length. Its body is elongated and laterally compressed, giving it a somewhat robust (deep-bodied) profile despite its modest size. The head is relatively small and narrow, with a subterminal (slightly upturned) mouth and large eyes set high on the head. Like other Pangasiids, it bears sensory barbels (“whiskers”) around the mouth: two long maxillary barbels on the upper jaw and additional barbels on the lower jaw. The maxillary barbels are especially long, typically reaching back to the base of the pectoral fins.

The skin and color of P. macronema tend toward a silvery gray tone. Unlike some related species, it generally lacks bold stripes or spots. FishBase notes that this species “lacks mid-lateral and abdominal stripes” and shows no black spot at the dorsal-fin origin. (Indonesian sources mention faint “lines” along the body and belly that meet near the pectoral fins, but these markings are subtle compared to the vivid bands seen in other Pangasius.)

The lancang’s fins are characteristic of its genus. The dorsal fin is short, with a single hardened spine followed by about seven soft rays. Just behind the dorsal fin lies a tiny adipose fin (a small fleshy fin common in catfishes), which is notably very small in this species. The pectoral fins are moderately sized, and the pelvic fins are placed well back on the body. The caudal (tail) fin is forked, reflecting its riverine, free-swimming habit. The anal fin is quite long – bearing roughly 30 to 38 soft rays – and in males it is especially large and elongated. Indeed, adult males can be distinguished by their unusually extended anal fins with elongated soft rays; after spawning these males often show reddish abrasion marks along their sides, likely caused by the sharp pectoral fin spines of females. This conspicuous sexual dimorphism (enlarged anal fin and side marks in males) is not seen in other Pangasius species.

The mouth of P. macronema is relatively small and set toward the tip of the head. Inside the mouth, the roof is armed with patches of fine teeth adapted for its diet. Specifically, there are four separate clusters of teeth on the palate – two on the vomer (anterior roof) and two or three on the palatine bones (posterior roof). These tooth patches help the catfish grasp and process soft-bodied prey. In addition, the first gill (branchial) arch bears a high number of slender gill rakers – typically 37 to 45 in adults – which filter small food particles from the water.

Overall, the lancang catfish reaches about 20–30 cm in length. Its mouth and fin structures, combined with its sensory barbels and gill rakers, suit it for a benthopelagic lifestyle in large tropical rivers. P. macronema often forms large schools in river channels and floodplain lakes, moving into tributaries and flooded forests in the rainy season. Its downward-facing mouth and tooth patches suggest a diet of benthic invertebrates: field observations note it feeding on mollusks, crustaceans, aquatic insects and small fish. The large eyes and long barbels of P. macronema enhance its ability to locate food in turbid waters. In sum, its streamlined yet deep-bodied form, extended anal fin (in males), and specialized mouthparts distinguish the species and reflect its role as a schooling catfish of Southeast Asian rivers.

Distribution and natural habitat

Pangasius macronema is found in widely separated parts of Southeast Asia. Its main strongholds are the great river systems of Indochina – notably the Mekong and Chao Phraya basins spanning Thailand, Laos, Cambodia and Vietnam – as well as isolated pockets in Indonesia. In Indonesia the lancang occurs on the island of Java and in southern Borneo (Kalimantan). Within these regions it inhabits large rivers and adjacent freshwater bodies. The species occurs along the banks of main channels, in river mouths, reservoirs and lakes, and it readily enters floodplain lakes, swamps and seasonally inundated forests during the rainy season. In other words, lancang favors deep, slow-moving waters and flooded habitats that are characteristic of tropical river systems.

The Mekong Delta in Long An Province, Vietnam: USAID Vietnam

Lancang are highly social, schooling fish. They are typically encountered in large groups cruising the current or resting under flooded river banks. Like many pangasiid catfishes, P. macronema is largely nocturnal – it becomes most active at night while hiding in burrows or shaded cover during daylight. During the monsoon flooding each year the lancang undertakes an upstream or floodplain migration. When rains fill the river and its floodplain, entire schools move onto inundated fields and forest pools. Here they exploit abundant food in the new waters. As the dry season returns, the fish gradually drift back into the main channels and deeper river pools to wait out lower flows.

Pangasius macronema is a generalist feeder. Its diet includes mollusks (snails and clams), crustaceans (such as shrimp), aquatic insect larvae (for example chironomid worms) and small fish. This varied diet is well-suited to life in the turbid, detritus-rich waters of tropical rivers. The fish’s morphology supports its feeding habits: it has long sensory barbels (whisker-like organs) extending beyond the pectoral fins and large eyes. Together, these adaptations allow the lancang to detect prey by touch and vision even when the water is murky. In fact, when floodwaters raise river turbidity, lancang tend to move into quieter backwaters, oxbow lakes or flooded forests alongside other species – a behavior thought to help them continue foraging when main-channel visibility is low. In short, Pangasius macronema is a nocturnal, schooling river catfish that has evolved to thrive in fluctuating tropical floodplain environments, feeding opportunistically on benthic invertebrates and small fishes while navigating the muddy, low-visibility waters of its habitat.

In the Mahakam waters of Indonesia, local fishermen often rely on the rengge a traditional gillnet that intercepts swimming fish, entangling them as they attempt to pass through its fine mesh: Luhkan Kota Banjarmasin/Nur Hidayat Eko Prasetyo

Feeding behavior and ecological role

Pangasius macronema is an opportunistic freshwater predator. Its diet includes benthic and nektonic prey such as mollusks, small crustaceans (shrimp and prawns), aquatic insects (especially chironomid larvae), and small fish. These food items reflect the species’ broadly omnivorous diet, characteristic of many riverine catfishes. To locate hidden prey in its often-muddy habitat, P. macronema relies on its long sensory barbels. The maxillary barbels extend nearly to the pectoral fins, serving as tactile and chemical sensors that help the fish detect food by touch and taste even when visibility is very low.

As a mid-level predator, Pangasius macronema helps regulate populations of benthic invertebrates and small fishes in its ecosystem. By feeding on detritivores and algae-eating organisms, it can indirectly influence the abundance of these groups and thus contribute to water quality and nutrient cycling. Ecologists sometimes describe such predators as “community balancers,” since by preying on common species P. macronema prevents any one prey group from becoming overly dominant. In this way, the species promotes biodiversity and helps maintain the stability and health of the freshwater community.

While it shares its genus with several other catfish species across Southeast Asia, Pangasius macronema stands apart in ways that are both subtle and significant. In particular, it differs from its close relative, Pangasius nasutus, in key aspects of morphology and geographical distribution. The closely related Pangasius nasutus differs from P. macronema in several key features:

• Dorsal fin: P. nasutus has two dorsal-fin spines, whereas P. macronema has only one.
• Size: P. nasutus grows much larger (up to about 90 cm total length), while P. macronema reaches only about 30 cm.
• Snout: P. nasutus has a longer, more pointed snout (the name nasutus means “long-nosed”), in contrast to the relatively short snout of P. macronema.
• Coloration: P. macronema has a silvery body without distinct lateral stripes or spots, whereas P. nasutus is uniformly grayish-silver.
• Maturity: P. nasutus attains maturity at a larger size than P. macronema, consistent with its heavier body mass.

Click here for the full article on Pangasius nasutus.