An adult giant salmon carp, of a fish species known by its scientific name Aaptosyax grypus that can grow as large as 30kg, has been documented for the first time in 18 years.

The nearly 1m long fish, weighing almost 6kg, was discovered in a wet market earlier this year near the Mekong in Stung Treng province.

A joint press release by the US Agency for International Development (USAID), the University of Nevada and the Fisheries Administration (FiA) confirmed recently that “One of the world’s most threatened fish species has been unexpectedly re-discovered in northern Cambodia”.

No adult giant salmon carp has been officially recorded since 2004, until it was discovered near the Mekong, the only river system on Earth where the species lives.

The press release added that the discovery confirmed the return of the breed to Cambodian waters. The merchant contacted Chan Sokheng, a biologist with the Cambodian FiA. From photographs, Sokheng was able to identify it as a giant salmon carp based on its sharply curved jaw, a yellow stripe on its head, and a shape reminiscent of a salmon.

Chhut Chheana, communications coordinator at the USAID-funded Wonders of the Mekong, told The Post on October 2 that the fish is in Stung Treng province.

The press release added that scientists would use the DNA of the dead fish to develop various tools for studying the distribution of the species. They also hope to find more specimens alive that can be tagged and released for further study.

Zeb Hogan, a University of Nevada, Reno fish biologist who leads the Wonders of the Mekong research project, said that this year had been a grand slam for wildlife surprises on the Mekong, but the game is far from over and victories for biodiversity are still hard to come by.

“The discovery of yet another amazing, but highly endangered animal, in an area that supports the livelihoods and food security of millions of people, shows plain as day the urgent need for conservation programmes and the potential benefits of government, scientists, and local communities coming together to safeguard the wonders of the Mekong,” said Hogan.

So rare is the giant salmon carp, it has been referred to as a “Mekong Ghost”. It is listed as critically endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Although the fish was not found alive — with the cause of death unknown — its discovery has raised hope that the species still exists in the Mekong.

Sokheng said that after more than two decades of working on this topic, he was happy to confirm the existence of this unique animal.

The Mekong River, which runs through six Asian countries, is a global biodiversity hotspot and home to almost 1,000 different species of fish, including some of the world’s largest freshwater fishes.

The press release added that the river and its many tributaries, which sustain the livelihoods of tens of millions of people, have come under increasing pressure in recent years from dam building, overfishing and climate change, with the larger species of fish under particular risk.

Chea Seila, Wonders of the Mekong project manager, said the recent discoveries along the Mekong have been the result of outreach to local people, many of whom have a deep knowledge of and dependence on the river and its wild creatures.