Conservationists are celebrating the discovery and release back into nature of six highly endangered Mekong giant catfish in Cambodia.

The bumper catch in the Mekong River Basin has boosted hopes of a revival of the critically endangered species, which is among the world's largest freshwater fish.

Fishermen released the fish alongside officials from Cambodia's Fisheries Administration (CFA), smiling as they held up the animals — weighing up to 130 kilograms (287 pounds) each.

What the giant haul means

The USAID-funded Wonders of the Mekong conservation group said the capture of so many giant catfish over just five days was "a remarkable and unprecedented event."

"I've never heard of this before," said research biologist and project lead Zeb Hogan, from the University of Nevada

Reno.

"It's a hopeful sign that the species is not in imminent, like in the next few years, risk of extinction, which gives conservation activities time to be implemented and to continue to bend the curve away from decline and toward recovery."

"By tagging these fish, we gain critical information about their ecology, their migrations, their habitat...to try to help these fish survive in the future," Hogan said.

How bad is the plight of the giant Mekong catfish?

According to the IUCN Red List, the current population of the giant Mekong catfish is unknown but it is thought to have declined by around 80% in the past 13 years.

They now are only found in some stretches of the Mekong River and its tributaries, but in the past inhabited the length of the 4,900-kilometer (3,044 mile)-long river — from its outlet in Vietnam to its higher reaches in the Chinese province of Yunnan.

The Mekong, a critical Southeast Asian waterway has long been plagued by illegal fishing, habitat loss and plastic waste.

In addition, the Mekong River Basin become a tougher habitat to survive in because of dams, including so-called mega-dams, and climate change. These have had a devastating impact on water levels and upstream connectivity in the dangerously rare catfish's aquatic habitat.

rc/rm (AFP, AP, Reuters)