Stung Treng, Cambodia – What has long been one of the great wildlife mysteries – the identity of the world’s largest freshwater fish – appears to have been solved last week as fishers in northern Cambodia, working with an international team of scientists, discovered a 661-pound (300 kilos) giant freshwater stingray near a remote island in the Mekong River.

The startling size of the endangered fish, whose weight was confirmed by scientists as twice that of an average lowland gorilla, makes it larger than the 646-pound (293 kilos) Mekong giant catfish caught in Thailand in 2005, which was the previous record-holder for largest freshwater fish on Earth. Freshwater fish are defined as those that have spent their entire lives in freshwater, as opposed to giant marine species like tuna and marlin, or fish that migrate between fresh and saltwater like the huge beluga sturgeon.

A 661-pound (300 kilos) giant freshwater stingray caught and released near a remote island in the Mekong River is largest freshwater fish in the world. Photo courtesy Wonder of the Mekong and University of Nevada, Reno.
A 661-pound (300 kilos) giant freshwater stingray caught and released near a remote island in the Mekong River is largest freshwater fish in the world. Photo courtesy Wonder of the Mekong and University of Nevada, Reno.

The record-breaking stingray, which measured over 13 feet (almost four meters) from snout to tail, was hooked by a fisher from Koh Preah island south of the town of Stung Treng, in the Mekong River as it runs through northern Cambodia. Recognizing the importance of his catch, the fisher quickly contacted a team from the USAID-funded Wonders of the Mekong research project to help release the ray, an endangered species, back into the river.

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“This historic event highlights the success of USAID’s Wonders of the Mekong project,” USAID/Cambodia Acting Mission Director Hanh Nguyen said. “Cambodia is blessed with incredible biodiversity and we are proud of the team’s efforts to promote sustainable management and raise public awareness on the important role of the Mekong River.”

For Zeb Hogan, a fish biologist at the University of Nevada, Reno who leads the Wonders of the Mekong, the stingray find is evidence that the natural world can still yield new and extraordinary discoveries, and that many of the largest aquatic creatures remain woefully understudied.

“In 20 years of researching giant fish in rivers and lakes on six continents, this is the largest freshwater fish that we’ve encountered or that’s been documented anywhere worldwide,” Hogan, who is also the host of National Geographic’s “Monster Fish” television series, said. “This is an absolutely astonishing discovery, and justifies efforts to better understand the mysteries surrounding this species and the incredible stretch of river where it lives.”

The huge ray was fitted with an acoustic tag, technology that will enable biologists to learn more about the secretive creature’s elusive behavior, a first for a stingray in Cambodia.

“Tracking the fish and identifying critical habitats will help the Wonders of the Mekong project develop additional environmental safeguards for the river and its communities,” Sudeep Chandra, co-director of Wonders of the Mekong and also the director of the University of Nevada, Reno’s Global Water Center, said.

In collaboration with the Cambodian Fisheries Administration, the Wonders of the Mekong project established a network of fishers who agreed to report catches of giant and endangered fish, including stingrays. Last month, fishers in Koh Preah reported to the team that they had caught a 400-pound giant female stingray, which the research team then helped release safely into the depths of the river.

“Fishers now cooperate with our project when they find giant stingrays so that we can tag and release them,” Chea Seila, program manager for Wonders of the Mekong, said. “These successful releases illustrate the importance of partnerships with local communities. Together, we all have an important role to play in fisheries monitoring and conservation.”

For the world record fish, fishers called to inform the team that a “much bigger” ray had been caught during the night of June 13. The stingray was safely returned to the river, it appeared strong and healthy as it quickly descended into the murky depths of the Mekong.

A crowd that included international scientists, Cambodian fisheries officials, and community fisheries members gathered for the release of the large female stingray, which they named “Boramy,” or “full moon” in the Khmer language, because the round-shaped fish was released at dusk with the moon shining on the horizon.

“The discovery of this world record stingray indicates the special opportunity we have in Cambodia to protect this species and its core habitat,” said His Excellency Poum Sotha, Delegate of the Royal Government, Director General of the Fisheries Administration. “In partnership with the Wonders of the Mekong project, and together with other countries in the Lower Mekong Basin, the Inland Fisheries Research and Development Institute of Cambodian Fisheries Administration will host a meeting to map out a regional species conservation action plan and solidify safeguards for the river, wildlife, fisheries and local communities.”

“Research is vital to solving today’s conservation and development challenges,” Mary Melnyk, who leads USAID Asia’s Environment Division, said. “Wonders of the Mekong research will be used to identify how best to safeguard the species and productivity of the Mekong River as it’s affected by both climate change and growing demands for infrastructure development.”

This hotspot has conservation measures in place, including community fish reserves, fishing restrictions in freshwater dolphin habitat and river guards. But the stingrays are also vulnerable to changes throughout the Mekong river basin such as pollution, habitat fragmentation and unsustainable hydropower development. In Thailand, populations have plummeted with mass mortality events due to water pollution and disrupted life cycles from river alterations.

Worldwide, more than 30 species of freshwater grow to over six feet long and more than 200 pounds. They are a diverse array of remarkable freshwater creatures, from air-breathing  500-pound plus arapaima to 325-pound alligator gar and carp as big as grizzly bears. There is cause for concern, as recent studies show that global populations of giant freshwater species have plummeted by almost 90% in the past four decades—twice as much as the loss of vertebrate populations on land or in the oceans.

“This record fish highlights the important connection between people, fish, and freshwater. It is a signal to us to protect our rivers and lakes. Large fish are bellwethers of the health of freshwater ecosystems worldwide – the fish are sending us a message and we need to listen to it.” Hogan said.

Reaching all 25 Cambodian provinces, USAID works with Cambodian and international partners to make the country a more open, prosperous, resilient, and inclusive partner in the Indo-Pacific region. USAID support focuses on advancing government accountability and human rights; improving health and nutrition; supporting education and child development; increasing agricultural production and food security; conserving forests and watersheds; helping farmers and households adapt to and mitigate the impacts of climate change and natural hazards; and assisting Cambodia’s response to the COVID-19 pandemic. For further information, visit

The University of Nevada, Reno, is a public research university that is committed to the promise of a future powered by knowledge. Nevada’s land-grant university founded in 1874, the University serves 21,000 students. The University is a comprehensive, doctoral university, classified as an R1 institution with very high research activity by the Carnegie Classification of Institutions of Higher Education. Additionally, it has attained the prestigious “Carnegie Engaged” classification, reflecting its student and institutional impact on civic engagement and service, fostered by extensive community and statewide collaborations. More than $800 million in advanced labs, residence halls and facilities has been invested on campus since 2009. It is home to the University of Nevada, Reno School of Medicine and Wolf Pack Athletics, maintains a statewide outreach mission and presence through programs such as the University of Nevada, Reno Extension, Nevada Bureau of Mines and Geology, Small Business Development Center, Nevada Seismological Laboratory, and is part of the Nevada System of Higher Education. Through a commitment to world-improving research, student success and outreach benefiting the communities and businesses of Nevada, the University has impact across the state and around the world. For more information, visit

The Cambodian Fisheries Administration works to maximize the contribution of fisheries to the achievement of national development objectives, especially those related to improving rural livelihoods of the poor, enhancing food security, the sustainable development and equitable use of the fisheries resource base. Fisheries in Cambodia constitute both an integral part of rural livelihoods and a major contributor to the national economy and food security. Fish provide more than 75 % of the total animal protein intake in people’s diets and provide nearly more than 1.5 million full time jobs and involve at least 6 million people in fishing activities.

Zeb Hogan, leading the Wonders of the Mekong project,is a research professor in the College of Science at the University of Nevada, Reno, a conservation biologist and a National Geographic Explorer. He had traveled the globe to find, study and protect monster freshwater fish – fish over six feet in length and more than 200 pounds. His book “Chasing Giants, The Search for the World’s Largest Freshwater Fish” is due out in April 2023.