World's Largest Freshwater Fish Documented in Cambodia's Mekong River

STUNG TRENG, Cambodia — In a monumental achievement for freshwater biology, scientists and local fishers in northern Cambodia have documented the world's largest recorded freshwater fish: a giant stingray weighing an astonishing 661 pounds (300 kilograms). The female stingray, measuring nearly thirteen feet from snout to tail, was safely captured, studied, and released back into the murky depths of the Mekong River. This extraordinary find highlights the critical ecological importance of the Mekong basin, a global biodiversity hotspot that continues to surprise researchers despite facing severe environmental pressures.

The historic discovery occurred when a local fisher on the island of Koh Preah contacted the Wonders of the Mekong project, a joint Cambodian-American research initiative. Recognizing the extraordinary size of the specimen, scientists rushed to the site to assist. The team fitted the massive ray with an acoustic transmitter before releasing her back into the river. This tracking device will allow researchers to monitor her movements and map crucial habitats within the river system, providing invaluable data for future conservation strategies.

Dubbed "Boramy"—which translates to "full moon" in the Khmer language, referencing both her circular shape and the timing of her release—the giant freshwater stingray (Urogymnus polylepis) has become a symbol of hope for conservationists. For decades, scientists have warned that the Mekong's unique megafauna, including the giant catfish and giant barb, are on the brink of extinction. The presence of such a massive, healthy specimen suggests that the deep pools of the Mekong still harbor viable habitats capable of supporting these ancient giants.

However, the discovery also underscores the urgent need for environmental stewardship. The Mekong River, which flows through six Asian nations, faces unprecedented threats from upstream hydroelectric dams, overfishing, agricultural runoff, and plastic pollution. These factors disrupt the natural flood cycles and destroy the spawning grounds essential for migratory fish. Researchers argue that protecting these deep pools, which act as dry-season refuges for diverse aquatic species, is vital for maintaining the food security of millions of people who rely on the river's resources.

By collaborating directly with local fishing communities, conservation groups are fostering a culture of co-management along the river. The successful release of Boramy demonstrates that community-led conservation initiatives can yield significant scientific breakthroughs. As data from Boramy's acoustic tag begins to stream in, scientists hope to unlock the mysteries of how these elusive giants navigate the complex river network, ensuring that the Mekong remains a vibrant, living ecosystem for generations to come.