Two decades ago, Zeb Hogan was working on Southeast Asia’s Mekong River when he got the idea for the Megafishes Project, a quest to find, study and protect the world’s largest freshwater fishes. At the heart of the project was the question: Which species is the largest? “I thought there would be a simple answer,” says Hogan, a fish biologist at the University of Nevada, Reno. “I was wrong.”

For years, he scoured Earth’s waterways, often as the host of Nat Geo Wild’s “Monster Fish” show. Although he came close on many occasions, he could not find a fish with a verified weight greater than a 646-pound Mekong giant catfish caught in Thailand