Zeb Hogan is a prominent biologist and freshwater fish researcher. He has spent many years investigating and searching for giant fish species in rivers and lakes around the world.
Two decades ago, fish biologist at the University of Nevada, Reno, and National Geographic explorer Zeb Hogan was working in the Mekong River in Southeast Asia when he came up with the idea for the Megafishes Project, an effort to locate, study, and protect the largest freshwater fish species in the world. The core question of the project is: What is the largest freshwater fish species?
The giant freshwater stingray currently holds the record for the largest freshwater fish in the world. (Photo: Zeb Hogan).
For many years, Hogan has scoured the waterways on Earth. However, he has yet to find a fish heavier than the Mekong giant catfish weighing 293 kg caught in Thailand in 2005. Instead, the biologist found that giant river fish around the world are largely understudied, and many species are severely declining, with some on the brink of extinction.
Last year, Hogan’s research team in Cambodia received a call from fishermen reporting that they had caught a giant freshwater stingray in the Mekong River, significantly larger than any previously caught. The stingray measured 4 meters in length and weighed 300 kg, and was recognized by the Guinness World Records as the largest freshwater fish in the world in 2022.
This discovery bolstered conservation efforts aimed at protecting this colossal species. Unlike the giant catfish that was killed and sold for meat in 2005, the stingray caught last year was released alive after being fitted with tracking equipment. This allows researchers to monitor its movements to learn more about a species about which little is known. “Now we have the tools to study and protect these magnificent fish. It’s not too late; the big fish are still out there,” Hogan shared.
In a project funded by the National Geographic Society, Hogan has identified over two dozen species that can be classified as “megafishes,” which are freshwater fish that can be at least 1.8 meters long or weigh 90.7 kg. They come in a variety of shapes and histories, from carp and catfish to electric eels and gharials. Common among them is that, besides their massive size, many species are experiencing population declines due to overfishing, dam construction, pollution, invasive species, and climate change. For example, the Chinese paddlefish, which can grow over 6 meters long, was declared extinct early in Hogan’s research.
Giant fish are indicators of the health of river ecosystems, so their decline is a concerning sign for freshwater ecosystems worldwide. After initially focusing on the Mekong giant catfish at the beginning of his career, Hogan suspects that this species, along with the arapaima, the largest carp species in the world, has disappeared from the Mekong River. Other contenders for the title of largest fish include the arapaima living in the Amazon River basin in South America and the European catfish.
For Hogan, the search for the largest freshwater fish is not yet over. “This stingray is likely not the largest individual existing in the river. Fishermen have told me that they have caught even larger stingrays. Some experts believe that other species, particularly the arapaima, could reach weights similar to that of the stingray. Studies of growth rings on the scales of arapaima in the Essequibo River in Guyana indicate that they could weigh more than their counterparts living in central Brazil,” Hogan shared. For instance, the relationship between length and weight suggests that a long arapaima caught two years ago in Brazil, measuring about 3 meters and weighing 245 kg, would weigh over 318 kg if it were in Guyana.
