The “Mekong ghost” fish is no longer a phantom. Similar to the mythical Rip Van Winkle, who wandered into the woods and disappeared for two decades, the giant salmon carp (Aaptosyax grypus) of Southeast Asia’s Mekong River seemed to vanish into folklore. This megafish had not been documented since 2005, leading many to assume it had quietly gone extinct. However, scientists have now confirmed the discovery of three individuals, caught between 2020 and 2023 in Cambodian waters. These findings rekindle hope for the giant salmon carp’s survival, as reported by fish ecologist Bunyeth Chan and colleagues in the November issue of Biological Conservation.
In their quest to find the elusive species, the researchers collaborated closely with local fishing communities, spreading the word that they were seeking “pa sanak,” the local name for the carp. In 2020, a fisherman contacted the Cambodian Fisheries Administration about an unusual catch. However, with only photographs, scientists could not definitively confirm its identity. Then, in 2022 and 2023, scientists obtained two more specimens caught by fishermen, finally confirming they had encountered a long-lost species. “I was incredibly surprised and thrilled to see Aaptosyax in the Mekong after its prolonged absence,” says Chan, from Svay Rieng University in Cambodia.
The giant salmon carp, characterized by its hooked jaw and salmon-like body, can grow up to 1.3 meters long and weigh over 30 kilograms. Its habitat, the Mekong River, boasts more megafish than any other river, including the Mekong giant catfish and giant freshwater stingray. Yet, the future of these river giants is precarious. Many megafish, including the giant salmon carp, are migratory species that depend on seasonal movements to feed and reproduce. However, dams constructed throughout the Mekong system have disrupted these migrations. Overfishing and climate change further imperil their survival.
The discovery of the three new giant salmon carp outside their presumed historic range suggests the species may be more widespread than previously believed. Cambodia has now officially listed the giant salmon carp as a protected species. Researchers hope this rediscovery will also prompt renewed efforts to safeguard the Mekong’s delicate 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 most biodiverse regions on Earth.”
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