Last year, a fisher caught the world’s largest freshwater fish, a Mekong giant stingray, in the Mekong River in Cambodia. After tracking the fish for a year, researchers are publishing research about the mysterious species.

In June 2022, in a remote location in Cambodia, a fisher reeled in a massive giant freshwater stingray. The fisher contacted researchers from the USAID-funded Wonders of the Mekong project, a project aimed toward protecting the unique Mekong River, the fish that occupy the river and the fishing communities that rely on the health and productivity of the river.

Upon arriving to the site of the record-breaking catch, the Wonders of the Mekong team attached an acoustic tracking device to the fish. The project had been working on deploying tracking technology that enables the researchers to study the movement of fish and where they reside, and the giant stingray was the first fish to be fitted with the device.

The University of Nevada, Reno’s Global Water Center is part of the international collaborative Wonders of the Mekong project. Students and faculty from the Global Water Center have traveled to Cambodia many times to support research projects, collect data and release fish.

The elusive giant freshwater stingray has been listed as endangered by the International Union for Conservation of Nature, but in Cambodian parts of the Mekong River, populations of the fish seem to be relatively stable. However, the species faces threats from habitat fragmentation by potential construction of hydropower dams, pollution and overfishing. The Cambodian government recently proposed establishing the Mekong River as a UNESCO World Heritage Site which would bolster conservation efforts.

Now, after collecting data for a year, Wonders of the Mekong researchers are publishing their work in a special issue of Water, a peer-reviewed, open access journal. This issue, titled “Endangered Fish, Rivers at Risk: Spatial Aspects of Freshwater Biodiversity Conservation,” will feature three articles from the Wonders of the Mekong team.

“The information we are learning about the stingray and other critically endangered fish is crucial not only to our efforts to ensure the survival of the world’s largest freshwater fish, but also the preservation of an area of great fisheries production that provides food for millions of people,” says Zeb Hogan, a biology professor at the University of Nevada, Reno, who leads the Wonders of the Mekong research project that initiated the study.

The first research article shares data about the movements of nearly 300 fish in the Mekong River that represent 27 species, including the giant freshwater stingray, and how the building of proposed hydropower dams on the Mekong River could affect the fish and the impacts of designating the Mekong River in Cambodia as a UNESCO World Heritage site could have on the region.

The second article is a review that compiles all the known information about the giant freshwater stingray. The research includes interviews with local fishers who have reported even larger fish than the record-breaking fish caught last June. There is the possibility that there is a different species of freshwater stingray, but more research needs to be conducted. The review highlights how understudied the fish is.

The third research article discusses how tracking information can be useful in designating fish reserves for conservation of the Mekong giant freshwater stingray. Using the acoustic tracking information, researchers show that the giant freshwater stingray they tagged typically stayed within the same deep pool of water, meaning that the establishment of fish reserves could be critical for the fish.

The research collected about the giant freshwater stingray will contribute to policy decisions made about the Mekong River, helping to protect the fish and people that rely on the Mekong.