AT A GLANCE
- Common Name: Iridescent Shark
- Scientific Name: Pangasianodon hypophthalmus
- Category: Fish
- Subcategory: Catfishes
- Range: Southeast Asia, native to the Mekong, Chao Phraya, and Maeklong river basins in Thailand, Cambodia, Laos, and Vietnam
- Habitat Type: Deep pools of large tropical freshwater rivers, seasonally flooded river floodplains, backwaters, and main river channels
- IUCN Red List Status: Endangered
- Lifespan: 15 to 20 years
- Diet: Omnivorous (aquatic plants, algae, zooplankton, aquatic insects, mollusks, crustaceans, and small fishes)
- Average Size/Weight: Total length 80 to 130 cm; weight 15 to 44 kg
- Key Defining Feature: Large, torpedo-shaped migratory catfish with a shark-like dorsal fin, smooth scale-free skin, down-turned low-set eyes, and a shimmering metallic silver sheen along its flanks
Overview
The Iridescent Shark (Pangasianodon hypophthalmus), also widely known as the Pangasius Catfish or Sutchi Catfish, is an iconic, large, and highly migratory river catfish in the family Pangasiidae. Despite its shark-like silhouette and popular aquarium trade moniker, it is not a cartilaginous shark, but rather an advanced freshwater teleost native to the mighty river arteries of the Mekong and Chao Phraya in Southeast Asia. Revered as one of the most culturally and economically vital food fishes in Asia, it undertakes immense seasonal spawning migrations across thousands of kilometers.
Biology and Physical Characteristics
Pangasianodon hypophthalmus has an elongated, laterally compressed, hydrodynamic body with completely smooth, scaleless skin. Its head is broad and flattened, characterized by an unusual facial arrangement: its eyes are situated remarkably low on the sides of the head, beneath the level of its mouth (hypophthalmus meaning ‘under eyes’). It has two pairs of delicate sensory barbels on the chin and snout. Juveniles display a dazzling, iridescent metallic silver-blue sheen with two bold dark longitudinal stripes along the lateral line; as the fish matures into a massive adult, it transforms into a uniform, majestic slate-grey to dark steel-blue with a gleaming white abdomen.
Behavior and Ecology
Intensely pelagic and continuously active, the Iridescent Shark swims incessantly in the open water column of deep river channels. It is a potamodromous migrant: as monsoon floodwaters rise between May and July, adults embark on colossal upstream migrations to rocky rapids and turbulent river stretches in northern Cambodia and Laos to spawn, releasing millions of adhesive eggs that drift downstream onto flooded river plains. Adults are generalist omnivores that feed on river weeds, snails, and fallen fruit during monsoon floods, retreating to deep, bedrock refuge pools during the dry season.
Conservation and Human Impact
The wild Iridescent Shark is classified as Endangered on the IUCN Red List. Wild populations have crashed precipitously over the past three decades due to the construction of major mainstream hydroelectric dams on the Mekong River, which block critical upstream spawning migrations, as well as historical overfishing. Conversely, it is one of the most heavily farmed aquaculture fishes in the world, with millions of tons produced annually in Vietnamese aquaculture ponds under the commercial name ‘Swai’ or ‘Basa.’
Interesting Factoid
Despite its shark-like fins and name, the Iridescent Shark is actually a gentle, giant catfish that migrates hundreds of miles up the Mekong River every monsoon season to lay its eggs.