Project Giant Fish researchers catch Big Macs in the Mekong River in northern Cambodia

The 300-kilogram Chaffee narrow-tailed stingray, the largest freshwater fish on record, was temporarily removed from the water for weighing. Locals and researchers quickly carried out the measurement and poured water on it before releasing it.

Cambodia, Mekong – Mur. Moul Thun knew that the giant freshwater stingray at the end of the line was bigger than any fish he'd ever seen before. But what the 42-year-old fisherman from Kaoh Preah, a remote island on Cambodia's upper Mekong River, didn't know was that the stingray would eventually be dubbed "the world's largest freshwater fish on record."

For Zebu, which has been recording large freshwater fish for nearly 20 years. For Zeb Hogan, finding the stingray that had been released gave him hope.

Hogan, a fish biologist and National Geographic explorer at the University of Nevada, Reno, said: "It proves that these critically endangered underwater behemoths still exist."

Hogan's quest for big fish is called the Megafishes Project and is supported by the National Geographic Society. The project began in 2005 when fishermen in northern Thailand caught a 293-kilogram Mekong giant catfish in the Mekong River, and Hogan, who has studied Mekong giant catfish in Southeast Asia for years, immediately determined that it was the largest and heaviest individual ever caught there. This also made Hogan wonder: Will there be bigger river behemoths elsewhere?

To find out, Hogan began searching rivers around the world and was a frequent host on National Geographic's "Monster Fish." But the answer to the question is more elusive than Hogan expected, not only are fishermen prone to exaggeration, but also logistical difficulties such as a lack of scientific information about freshwater fish, unverifiable evidence, and old drawings and photographs.

Although he has encountered countless giants such as arapaima, which breathes air directly in the Amazon and wels catfish, which eats pigeons, Hogan still can't find any scientifically based freshwater fish catch records that can surpass the Mekong giant catfish that inspired him to embark on the "fish hunting road" in the first place.

It wasn't until about two weeks ago that Wonders of the Mekong, a research group led by Hogan in Cambodia and supported by the U.S. Agency for International Development (USAID), received a message from Mur. Thun's phone. Thune told the team that he accidentally caught a giant freshwater stingray that was "much bigger" than any stingray he had ever seen, perhaps even a completely different species.

Upon arrival at Kaoh Preah, the team determined that Thun had caught a healthy Chaffee narrow-tailed stingray female, and that Thun was quite accurate in his body size. The Chaffee narrow-tailed stingray was more than 3.96 meters long from snout to tail, and after the research team measured it on three side-by-side scales, it shocked researchers with a weight of 300 kilograms and set a world record.

The Guinness World Record confirmed the record on June 24 and declared the Chafee narrow-tailed stingray from Kober Island the largest freshwater fish ever recorded, and the world's largest freshwater fish species alongside the Mekong giant catfish.

Ancient creatures

Project Giant Fish originally aimed to find, study and protect the world's largest freshwater fish. The plan focuses on species that grow at least the size of a human – at least 1.8 meters or 90 kilograms – and live only in freshwater, such as the beluga sturgeon, which migrates between freshwater and salt water. At the beginning of the project, Hogan drew up a list of about 30 species and focused on them.

But Hogan soon learned that the challenge with the program was that many of the species on the list were hard to find. They live in remote, hard-to-reach places and often in murky waters; Sometimes even people who have lived in giant fish habitats all their lives have never heard of these creatures, let alone seen them. In addition, at the beginning of the search, the number of scientists studying these giant fish was relatively rare.

But what is clear is that the number of these river behemoths is dwindling under a range of threats. Things like overfishing, competition for food from alien species, water pollution, and dams that prevent these fish from migrating to complete their life history.

Studies have shown that populations of freshwater megafauna worldwide are declining twice as much as terrestrial or marine vertebrates, and many giant fish are critically endangered. For example, the blockbuster candidate for the world's largest freshwater fish, the Chinese paddlefish, went extinct in the early stages of Hogan's search.

As Hogan's plan continued to grow, the focus gradually shifted to conservation. "The point is never to find the big fish, but to find ways to protect these extraordinary animals," Hogan said. Certain fish have been living on Earth for hundreds of millions of years, but are now disappearing."

Record-breaking stingrays

There are dozens of species of freshwater stingrays, and Hogan has always suspected that the largest river behemoths must come from this family. On a trip to Argentina to shoot In Search of the Super Big Fish, Hogan caught a short-tailed river stingray about 181 kilograms, but he knew that Chafee narrow-tailed stingrays in Southeast Asia could grow much larger than that.

For several years, Hogan and a Thai research team studied stingrays in two rivers near Bangkok. During this time, the team caught several stingrays that appeared to be large enough to rival the Mekong giant catfish in 2005, but Hogan and his colleagues never knew their exact weight.

By 2016, chemical contamination of Thailand's upper Mekong River killed at least 70 giant stingrays. When scientists returned to the river two years later, they found that not only had the overall number of stingrays declined, but there were hardly any large stingrays.

Recently, Hogan's "Miracle of the Mekong" program has accelerated the pace of research in northern Cambodia. Both sides of the Mekong are highly biodiverse seasonally flooded forests, believed to be home to up to 200 billion fish a year, and are considered an important sanctuary for many Mekong giant fish, including the Chaffee narrow-tailed stingray, during the dry season.

The research team worked with local communities to build fisherman networks and encourage fishermen to report their catch before releasing stingrays and other endangered species. Although it is not illegal to catch stingrays in Cambodia, they are not considered very tasty, so they are rarely considered a target species; However, it is inevitable to accidentally take the bait occasionally, just like the record-breaking female caught on the night of June 13.

After receiving a call from Thun, team members based in Phnom Penh, Cambodia's capital, quickly rushed to the riverbank and met with a team of American scientists who were also doing research there. Researchers quickly implanted sound transmitters in the tails of stingrays, hoping to provide a glimpse into the species' elusive behaviors, such as where they feed, migrate and give birth.

"This call from Thun confirms the importance of working with local communities, and fishermen can be great allies in protecting these animals," Hogan said.

By the time the stingrays were to be returned to the river, a group of people, including Cambodian fisheries officials and village supporters, had already gathered. Many of them were busy photographing the giant creature, which scientists named "Boramy" (Khmer for "full moon") because its body is disc-shaped and falls on the day of the wild release, a name often used to describe beautiful women.

A sign of hope

For Hogan, the section of the Mekong River where the stingray was found is not only a potential hotspot for Chaffee narrow-tailed stingrays, but also a source of hope for all threatened giant fish. Hogan said that despite the bad situation of giant fish in many of the world's rivers, there are still reasons for optimism.

For example, conservation efforts in North America have helped populations of several large freshwater fish, such as alligator gar and lake sturgeon, to recover; Similarly, indigenous communities in the Amazon have restricted fishing for arapaima, the big air-breathing creatures.

"When people discover the existence of these animals and start appreciating how incredible they are, they are inspired." "The record-breaking fish in 2005 was finally cut into pieces of meat and sold, but now we are using the transmitter to track the world's largest freshwater fish," Hogan said. It is this before and after comparison that means that there is still hope for all this."