A colossal megafish once believed to be extinct was recently found in Asia's famed Mekong River, according to a report relayed by Phys.org.
Between 2020 and 2023, fishermen in the Cambodian region of the Mekong caught three giant salmon carp (Aaptosyax grypus). Before this, the species' last confirmed sighting was in 2005.
Scientists announced the return of the species in a recent study published in the journal Biological Conservation. The authors credited local fishing communities with alerting them to the rare catches and turning over the specimens for evaluation.
"I was really surprised and excited to see the real fish for the first time," Bunyeth Chan, study co-author and researcher at Svay Rieng University in Cambodia, said, according to Phys.org.
This species of megafish is especially recognizable due to a knob at the tip of its lower jaw and a patch of yellow around its large eyes. According to Science News, the rare fish can grow up to 4 feet and weigh more than 66 pounds.
"The giant salmon carp is like a symbol of the Mekong region," Chheana Chhut, study co-author and researcher at Inland Fisheries Research and Development Institute, according to Phys.org.
The 3,000-mile Mekong River is home to more megafish than any other river in the world, Science News reports. However, it is also a hot spot for industrial pollution and overfishing, which has devastated fish populations in the region over the past decades. A recent study found that as much as one-fifth of fish species in the Mekong face extinction due to unsustainable development, including hydropower.
The scientists also noted that the Mekong is exceedingly difficult for fish to navigate due to its more than 700 dams and other obstructed passageways. Dams use the flow of moving water to generate electricity — but they alter the natural flow of water to work. This can impact water quality and block essential fish migration.
Like similar findings in California, where thousands of salmon were found dead near dams, the Mekong River's dams prevent fish from migrating and finding the food they need. This makes it difficult for species to thrive and get to historic breeding grounds to reproduce.
According to the study, freshwater megafish like the giant salmon carp are among the most globally threatened fish species, with an estimated population decline of 94% since 1970. Native fish are essential to their ecosystems, supporting biodiversity and acting as predators and prey.
In the study, the authors called for the "development of conservation planning and management of local protected areas" to help the megafish thrive in their environment. The authors also say they plan to work with local fishing communities in Thailand and Laos to confirm if the megafish still travel to other stretches of the Mekong as they once did.
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