Bungin, IndonesiaWe know that the whale shark is the biggest fish in the ocean, but what is the world’s largest freshwater fish? The answer to that seemingly simple question has remained a mystery as murky as the Southeast Asian rivers in which it’s most likely found.

Officially, the heavyweight title belongs to the Mekong giant catfish, with a specimen caught in northern Thailand in 2005 weighing an astounding 646 pounds. But researchers have long believed there are bigger fish out there, with a mysterious giant freshwater stingray being the top contender.

Now, there is increasing evidence they might be right. A recent survey of rivers in Indonesia suggests that a species known as the giant freshwater stingray may indeed grow much