The ‘Mekong ghost’ megafish has resurfaced after an extinction scare 

The “Mekong ghost” fish is a ghost no more.

Like the legendary Rip Van Winkle, who wandered into the woods and disappeared for 20 years, the giant salmon carp (Aaptosyax grypus) of Southeast Asia’s Mekong River also seemed to vanish into the depths of myth. The megafish had not been documented since 2005, leading many to believe the species had quietly slipped into extinction.

But scientists have now confirmed the discovery of three individuals, caught from 2020 to 2023 in Cambodian waters. The finds reignite hope for the giant salmon carp’s survival, fish ecologist Bunyeth Chan and colleagues report in the November Biological Conservation.

In their search for the elusive species, the researchers had worked closely with fishing communities, spreading the word that they were looking for “pa sanak,” the local name for the carp. In 2020, a fisherman contacted the Cambodian Fisheries Administration about an unusual catch. But with only photographs of the fish, scientists couldn’t definitively confirm its identity.

Then, in 2022 and 2023, scientists got their hands on two more specimens caught by fishermen, and confirmed they’d seen a ghost. “I was extremely surprised and excited to see the existence of Aaptosyax in the Mekong after its disappearance for so long,” says Chan, of Svay Rieng University in Cambodia.

The giant salmon carp, with its distinctive hooked jaw and salmonlike body, can grow up to 1.3 meters long and weigh over 30 kilograms. Its habitat, the Mekong River, is home to more megafish than any other river, including the Mekong giant catfish and giant freshwater stingray.

However, the future of these river giants remains uncertain. Many megafish, including the giant salmon carp, are migratory species that rely on seasonal movements to feed and spawn. But dams built throughout the Mekong system have disrupted these migrations. Overfishing and climate change further threaten their survival.

The fact that the three newfound giant salmon carp were discovered outside what was suspected to be their historic range suggests the species may be more widespread than previously thought. Cambodia has now officially added the giant salmon carp to its list of protected species. And researchers hope the rediscovery will also spark renewed efforts to safeguard the Mekong’s fragile ecosystem.

“This discovery,” says study coauthor Zeb Hogan, a fish biologist at the University of Nevada, Reno, who leads the USAID-funded Wonders of the Mekong project, “is not just about saving the salmon carp, but about protecting one of the greatest biodiversity hot spots on Earth.”