Iridescent Shark

Fascinating facts about the Iridescent Shark

• At a full-grown length of 130 cm (4.3 ft) and a weight of up to 44 kg (97 lb), the iridescent shark is actually a catfish.
• During the Mekong flood season, these fish surge upstream from May to July, then reverse course from September through December, timing their journey to the rise and fall of water levels. Their migration reveals a tight link between river dynamics and breeding cycles that many other fish ignore.
• A single year of Vietnamese pangasius exports topped US$1.8 billion in 2014, turning a low-priced white fish into a global commodity. The sheer market value underscores how a modest-tasting fish can drive major international trade.
• Aquarium hobbyists need tanks at least 12 m (39 ft) long for a healthy school, yet most home setups only allow 15–30 cm (6–12 in) growth, stunting the fish and often shortening its lifespan. This mismatch highlights how the pet trade can unintentionally compromise the well-being of a species that naturally roams large rivers.
• In August 2015, a stray iridescent shark was found in a Colombian tributary of the Magdalena River, a system home to over 200 native fish, 35 of them endangered. Its accidental arrival warns that moving a single species can threaten entire native communities.

At a glance

About the Iridescent Shark

The iridescent shark catfish, Pangasianodon hypophthalmus, dazzles with a shimmering, rainbow-tinged sheen in its juvenile years, a trait that earned it its name despite being a true catfish, not a shark. Adults grow to a formidable 130 cm (4.3 ft) and can weigh as much as 44 kg (97 lb), their bodies turning a uniform grey while the fins stay dark grey or black. Juveniles display a distinctive black stripe along the lateral line and a second stripe below it, a pattern that fades as they mature. Native to the great rivers of Southeast Asia, most notably the Mekong and Chao Phraya basins, these fish thrive in tropical freshwater with a pH of 6.5–7.5, water hardness of 2.0–29 dGH, and temperatures between 22 °C and 26 °C (72–79 °F). Their swim bladder doubles as an air-breathing organ, allowing them to survive hypoxic waters and undertake seasonal migrations: upstream from May to July in the Mekong, and downstream again from September through December, with regional variations near the Khone Falls. Iridescent sharks are opportunistic omnivores, feeding on crustaceans, smaller fish, and plant material, a diet that supports their massive aquaculture industry where they are marketed as swai, panga, cream dory or basa. Their migratory instincts and schooling nature make them a spectacular sight in the wild, often swimming alongside spot pangasius and red-tailed tinfoil barb. A surprising trait is their ability to tolerate rapid changes in oxygen levels, a resilience that paradoxically makes them vulnerable to modern hydropower projects, blade strikes, shear forces and turbulence can cause severe injury and mortality, a stark reminder that their very adaptability can become a liability in altered riverine landscapes…

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