Footage shot on 6 March during the making of wildlife programme Ocean Mysteries shows scientists examining a Giant Whiptail Stingray found in the Mae Klong River, Thailand.
The creature measures over 14ft long, 8ft wide and weighed over 800 pounds.
According to wildlife presenter Jeff Corwin, the ray may be the largest freshwater fish ever captured.
"So we're here in this incredible river system in Thailand. I'm with my good friend Dr Ning, she's a veterinarian and she has this really remarkable study unravelling the mysteries of the largest species of fresh water fish on the planet. This is a giant fresh water stingray. It is 14ft long, it's 8ft wide, it weighs probably 800 pounds.
"And she's done all this cool stuff with it. We have genetic samples, we've got the measurements, we put in an identification tracking device so we know where she goes. But the best news about this stingray is we've found out that she's pregnant and that's great news for this species and for its future.
"By the way, why do they call them stingrays? This is its defence. It has this very barbarous, potentially lethal defence. Only defence, not offence. And it's the spine, it's got venom, it can be up to 15 inches long and you certainly don't want to get nailed by it. But for the most part they are a gentle giant," he said.
During the investigation of the stingray, local scientist Dr Nantarika Chansue discovered the animal was pregnant.
Giant Whiptail Stingrays spend most of their time buried under sand to avoid predators and carry a defensive barb which can cause serious injury.
After various data was collected, the ray was released back into the Mae Klong River.