Giant freshwater stingray
Discovered in 2004
Experts believe that this fish, wide and flat in form, and sporting a long, whip-like tail, has changed little over many millions of years.
Where do they live?
The species is known to inhabit estuaries and large deep rivers, burying in sandy or silted river bottoms, to lie in wait for unsuspecting fish, clams and crabs, using a sensor that can detect an animal's electrical field.
Unusually, this species is occasionally sighted near urban centres of the region.
A very big ray
Scientists estimate that Himantura chaophraya can grow five metres and 600kg in size, certainly making it among the largest of the approximately 200 species of rays. The fish gives birth to live young measuring 30cm wide, so even the small ones are large!
Watch out for that barb
Though stingrays do not readily attack humans, they are one of the few Mekong giant fish that can pose a real danger to those who handle them. Their tail has a deadly barb at its base which can be as long as 38cm - the largest of any stingray - and can easily penetrate human skin and even bone, much like an arrow and typically inject poison.
Despite its mega dimensions and toxicity, surprisingly these nomadic species remain elusive and cloaked in mystery, only first being identified by scientists less than 20 years ago.
Chances for long-term survival are slim
Decades ago they were reported to be more common than they are now. This could be because of overharvesting, pollution and because their river habitats have degraded, and it appears they no longer inhabit some parts of their historical range.
Thai rivers have been plagued by serious pollution, overfishing and dam building, which have taken a deadly toll on Thailand's once diverse and abundant river life. The ray is believed to exist in only small numbers.
Populations of giant stingray are faring better than other Mekong giant fish. Experts suggest this may be because of the depth of the river these species inhabit as well as the fact that they are so difficult to catch.