Scientists tag and release giant freshwater stingrays (Urogymnus polylepis) in the Chao Phraya River basin in central Thailand. This endangered species inhabits giant rivers in regions from India to Indonesia. (PHOTOGRAPH COURTESY OF ZEB HOGAN)
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Zeb Hogan got the idea for the Megafish Project to find, study and protect the world’s largest freshwater fish 20 years ago while working in Southeast Asia’s Mekong River. At the core of the project was the question: “Which species is the biggest?” “I thought there was an easy answer,” says Hogan, a fish biologist at the University of Nevada, Reno. “It was a mistake”
For many years, Hogan scoured rivers around the world as host of the National Geographic Wild TV show “Find Monster Fish!”He came close many times, but in 2005 he caught a 293kg calf in Thailand that sparked his research.Mekong giant catfish(Pangasianodon gigas) could not be found. Instead, he found that the giant fish that live in rivers around the world are poorly studied, and in most cases are in serious decline, with some species on the brink of extinction.
Scientists tag and release a Mekong giant catfish (Pangasianodon gigas) in Cambodia’s Tonle Sap River. The Critically Endangered Mekong giant catfish can grow to be at least 2.7m long and weigh about 293kg. (PHOTOGRAPH BY ZEB HOGAN)
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Hogan’s research team in Cambodia then miraculously received word from fishermen that they had caught a giant freshwater ray, commonly known as the Himantura Chao Phraya (Urogymnus polylepis), much larger than anything ever caught in the Mekong River. rice field. As a result, the freshwater stingray is about 4m long and weighs about 300kg, and was certified by Guinness World Records as the world’s largest freshwater fish in 2022. (Reference article:“New world record for freshwater fish found with giant stingray weighing 300 kilograms”）
The discovery spurred freshwater ray conservation efforts. The 2005 catfish was killed and sold for meat, while the freshwater ray caught in 2022 was released alive into the Mekong River after being fitted with acoustic receivers. As such, researchers have been able to track the movements of the rays and learn more about the species’ biology, which until now was largely unknown.
“These giant fish have often gone extinct without us knowing,” says Hogan. “Now we have the means to study and protect these amazing creatures, so we need to put our newfound knowledge to good use in conservation. It’s not too late.” The giant fish is still out there.”
Hogan says he continues to search for fish that are even bigger than giant freshwater stingrays.
Candidates for the largest freshwater fish such as carp and catfish
In a project supported by the National Geographic Society, Hogan identified more than 24 species of freshwater fish that are over 1.8m long and weigh over 90kg, and named them “megafish.” There are a wide variety of fish with different shapes and life histories, such as giant carp, catfish, electric eels, and giant gars.
It’s not just their size that they have in common. The same goes for the rapid decline in populations due to overfishing, dam construction, pollution, invasive species, and climate change.Can grow to over 6m in lengthSpinner Sturgeon (Psephurus gladius)was declared extinct early in Hogan’s search. “It’s very upsetting that fish that have lived on Earth for hundreds of millions of years have gone extinct in our lifetime,” he says. (Reference article:“The largest freshwater fish, the spinner sturgeon, is extinct”）
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