A fisherman in northern Cambodia has caught what researchers say is the world’s largest freshwater fish – a giant stingray that scientists know relatively little about.
The fisherman, 42, caught the 661-pound fish – which was around 13ft long – near a remote island on the Mekong in the Stung Treng area. A team of scientists from the Wonders of Mekong research project helped tag, measure and weigh the stingray before it was released back into the river. The search party believe he was in good health when he was released and expect him to survive.
The beacon – which emits an acoustic signal – will allow researchers to track the movements of the fish and, they hope, learn more about the behavior of its species in the Mekong.
The catch “shows how little we know about many of these giant freshwater fish,” said University of Nevada fish biologist Zeb Hogan. “You have a fish that now holds the record for the largest freshwater fish in the world, and we know little about it.”
The fisherman, Moul Thun, caught the giant stingray with a hook and line on the evening of June 13, then contacted researchers the next morning.
Researchers from the Wonders of the Mekong were already in northern Cambodia installing underwater receivers as part of a project to monitor migratory fish in the river.
“It’s a particularly healthy stretch of the river with lots of deep pools – pools up to 300 feet deep,” said Hogan, who is also the host of National Geographic’s ‘Monster Fish’ TV series. “We began to focus on this area as a particularly important stretch of river for biodiversity and fisheries, and as the last refuge for these large species.”
For several months, the research group has been in contact with local fishermen, asking them to get in touch if they land a large catch. The group has contributed to two other large releases of giant freshwater stingrays in recent months. The fisherman who caught the record ray was paid market price for his catch.
“It works because the fish is not a highly prized food fish,” Hogan said.
Hogan said little is known about the giant freshwater stingray. The creature has a mouth about “the size of a banana” without teeth, but with “grasping pads” used to crush prey.
“They are at the bottom to find shrimps, molluscs and small fish. They can suck them in with that banana-shaped mouth and smash them,” Hogan said.
Fishermen reported three catches of female stingrays in the area in the past two months, Hogan said. Scientists suspect the site could be an important seasonal staging site for giant freshwater stingrays and could serve as a breeding ground for young.
The research group plans to tag and track a few hundred large fish in the Mekong to better understand fish migrations and local habitat in Cambodia’s upper Mekong.
“There is potential for hydroelectric development where these rays have been captured,” Hogan said. “We want to understand the importance of this area before there is development, potentially in an unsustainable way.”
Hogan said the Cambodian government has expressed interest in developing a conservation plan for giant freshwater stingrays.
The upper Mekong is also a habitat for the giant Mekong catfish and other species of large freshwater fish.
Worldwide, “most of these big fish species are struggling, their populations are declining. The Chinese paddlefish was declared extinct in 2020,” Hogan said. “We need to do more to protect these freshwater habitats.”
The former world record-holding fish – a 646-pound giant Mekong catfish – was also caught on the Mekong in 2005, in Thailand.
There are other larger recorded catches of fish that spend time in both freshwater and saltwater, such as beluga sturgeon.
“It’s the record for the biggest fish that has spent its entire life in fresh water,” Hogan said of the recently caught stingray.