A team of scientists were stunned when a rare species of fish – previously considered extinct in Cambodian waters – was caught by a fisherman near the Sesan II hydropower dam in Stung Treng province.

Thach Panara, head of the Laboratory, Inland Fisheries Research and Development Institute under the Fisheries Administration, told The Post that no examples of the Mekong giant salmon carp (Aaptosyax grypus) had been found in the Kingdom’s waterways in more than two decades. The administration’s fisheries resource team had supposed the fish extinct. The July 2 catch caught the team by surprise.

He said: “1999 was the last recorded sighting of the giant salmon carp in Cambodia. We did not expect to see their return.”

Panara said the giant salmon carp weighed 6kg, but unfortunately had died. The carcass was still a valuable resource for research, however. Scientists would thoroughly examine it for clues about the lifestyle of this rare species.

“We are sorry it’s dead, but it’s still important for us as scientists. This may indicate that they are still present in the freshwaters of Cambodia,” he added.

Panara told The Post that samples taken from the fish are currently being examined at his laboratory to determine whether the specimen was a pure giant salmon carp or a genetically engineered fish.

According to Chea Seila, programme manager for Wonders of the Mekong, the giant salmon carp is active, catches young fish as food and lives in the deep pools of the Mekong River in northeastern Cambodia bordering Laos and the central part of Thailand. Because the fish is active in swimming for prey, it is easily caught in fishing nets, and in the last decade, its numbers are estimated to have dropped by more than 90 per cent.

She added that now the population in Laos and Thailand are predicted to become extinct due to overfishing and the development of dams along the Mekong River causing the loss of their habitat.

“According to the most recent study – conducted in 2017-2018 – it was determined that the giant salmon carp was likely extinct in Cambodia and only to be found in the least number in Thailand and Laos,” she said.

However, the recent catch raised renewed hopes for the researchers and conservationists.

Seila added that although the exact location of the Cambodian population of the species had not been identified, the catch proved the fish is still present and more cooperation to rediscover this rare species is needed.

Kung Chanthy, chief of the community fishery network in Borei O’Svay commune of Stung Treng province’s Sen Chey district, said that because the giant salmon carp is so rare, the fishermen in his community, including himself, is unfamiliar with it. No fisherman had caught one in 20 years, he said.

“More than 20 years ago, I caught them every once in a while, but not often. As far as I remember, I mistook it for a [Luciocyprinus striolatus] cyprinid. My parents knew it well and told me it was the giant salmon carp and that its price was similar to that of the [Mekongina erythrospila] species,” he added.

The giant salmon carp can grow to a length of 130cm and weigh up to 30kg. It has small scales and a large mouth, similar to that of a tortoise, with a pronounced lower jaw. Unlike many of its deep freshwater cousins, this carp has no moustaches.

The species is classified as critically endangered on the International Union for Conservation of Nature (IUCN) Red List.