By Guy De Launey
BBC News, Phnom Penh
Four giant catfish, which were raised in captivity, have been released into the wild in a ceremony in Cambodia.
This is the catfishes' first taste of the wild
Scientists tagged the fish so they can follow their behaviour and try and find out why numbers have been declining.
The Mekong River Giant Catfish was once common in the Mekong and its tributaries, but is now listed as "critically endangered".
Conservationists worry the Mekong is facing serious ecological problems.
Scientists coaxed the four giant catfish into the water where the Mekong meets the Tonle Sap in Phnom Penh.
Then a boatload of photographers and TV cameramen overbalanced and followed them into the murky depths.
The stars of the show were unlikely subjects for a media scrum.
The Mekong giant catfish looks a little like a toothless, upside-down dolphin. But its plight is indicative of worrying trends in the Mekong eco-system.
For generations, Cambodian families have pulled fish out of the water almost at will.
But in recent years, there has been a drastic decline in catches, and estimates suggest that giant catfish numbers have fallen by 90% over the past two decades.
Possible causes include over-fishing, including the use of explosives and electricity, pollution and the building of dams upstream.
The WWF's Director-General, Claude Martin, hopes the release of the catfish will stimulate the authorities to take action.
"I don't think the four fish we've released today will make a big contribution to the viability of that population.
"It is certainly a species that is very vulnerable because it is a migratory species and many of the migratory species today are [affected by] the river system, particularly dams," he said.