One of the largest and rarest freshwater fish in the world was netted by local fishermen near Phnom Penh earlier this month.

A two-metre Mekong giant catfish, weighing an estimated 90 to 114 kilos, one of only a handful left of a species that faces extinction, was caught on November 9 in the river from which it takes its name.

“This is the first wild adult Mekong giant catfish seen in Cambodia this year,” said Zeb Hogan, a marine biologist at the US’s University of Nevada who was visiting Cambodia and was called in at the time of the catch. “It may be the first seen anywhere in the world in 2015.”

The find was especially significant, Hogan added, because it showed the animal, which can live up to 60 years, was still following its traditional route.

“This tells us that Mekong giant catfish are still making their annual migration out of the Tonle Sap Lake, down the Tonle Sap River, and into the Mekong,” he said.

But the development of dams in the region poses an existential risk to the species, he said.

“The Xayaburi dam in northern Laos, for example, would likely act as an impassable barrier to very large fish like the Mekong giant catfish and could drive it to extinction,” Hogan said.

Overfishing had also helped slash a population that has declined by as much as 99 per cent since the mid-1800s. “Because this fish lives so long, and is relatively slow to mature, it does not appear capable of supporting intense, unregulated fishing,” Hogan said.

Fishing for the giant catfish is banned throughout the region, but information gathering is inadequate, Hogan added.

“Neither Mekong giant catfish numbers, nor basin-wide harvest is closely monitored, so the impact of the moratorium is unclear.”

According to Hogan, a cross-border management plan is needed to save the fish, and should include protecting migratory corridors and habitat.

However, under-secretary of state at the Ministry of Agriculture Nao Thouk said tough laws were already in place to protect the endangered fish, and questioned the impact of dams.

“I don’t agree that dams such as the Xayaburi are such a big problem,” he said. “They will have some effect, but I think there is a separate population of the Mekong giant catfish in the area around Cambodia that will survive independently of the population in Laos.”