The Critically Endangered Mekong giant salmon carp Aaptosyax grypus was thought to be extinct in Cambodia, with no specimens reported from 2005 to 2020. However, three individuals were captured during 2020–2023, and one, weighing 6.2 kg, was captured on 27 November 2025 from the Sesan River below the reservoir in Pluk Commune, Sesan District, Stung Treng Province. The IUCN Red List assessment for A. grypus notes the species is possibly extinct in Cambodia, but the assessment is flagged as ‘Needs updating’. These recent records from the Cambodian Mekong provide evidence that the species persists in the country and indicate the need to revise the Red List assessment.

Since 2017, the Wonders of the Mekong Project, in collaboration with the Cambodian Fisheries Administration, has been implementing conservation programmes in the Cambodian Mekong that focus on several megafish species (i.e. body mass ≥ 30 kg), including the A. grypus. The project has built collaborations, networks and trust among fishing gear operators, local communities and fishers for reporting captures of threatened megafishes and for releasing them back into the wild, using financial incentives.

The locality of the most recent capture of A. grypus in the Cambodian Mekong overlaps with the locations of the 2020–2022 captures. Given the elusiveness of the species and the lack of knowledge on its distribution and ecology, it is necessary to promote community awareness to recognize, report and, if possible, release captured specimens, and to develop non-invasive detection methods (such as eDNA) to locate existing populations. As all four recently captured specimens were recovered dead from market vendors, they provide little information about the species, making it difficult to identify critical habitats, infer likely threats or target site-specific management actions.

These recent reports provide researchers and managers with justification for renewed action to locate and monitor remaining populations (e.g. via expanded community outreach and local-knowledge surveys, eDNA monitoring, and identification of priority river reaches for habitat protection) and to catalyse stronger management. The reports have already encouraged policy attention: Cambodia’s Fisheries Administration has listed A. grypus as threatened, making its capture and sale illegal. Additional support is now needed to expand outreach and efforts to conserve A. grypus and other threatened megafishes in the region. There is a need to establish a working group to develop conservation strategies for A. grypus, as was done for the Mekong giant catfish Pangasianodon gigas. We recommend inclusion of A. grypus under the Convention on Migratory Species, which is designed to promote coordinated conservation and management of species that undertake transboundary movements. The recent records in Cambodia suggest the species moves between Cambodia, Thailand and Lao PDR within the lower Mekong basin, and would therefore benefit from regional cooperation on monitoring, threat reduction and protection of key river reaches and migration corridors.