Rediscovery and future approaches to conservation of the elusive giant salmon carp Aaptosyax grypus, a Critically Endangered megafish in the Mekong

The Critically Endangered giant salmon carp (Aaptosyax grypus) is an endemic mega fish from the Mekong River basin. It had not been recorded in the wild since 2005, and was considered as possibly extinct. Here, we report the capture of three new specimens between 2020 and 2023. Those recent observations indicate that the species persists, and that one or more populations of A. grypus inhabit the Cambodian Mekong and its tributaries. Though the rarity of A. grypus makes it difficult to set specific conservation actions, we suggest building on the recent development of environmental DNA techniques and citizen science to investigate A. grypus geographic range and habitats as a first step before initiating actions to conserve its habitats. Given the emblematic species status of A. grypus, its conservation could have an umbrella effect contributing more broadly to the conservation of the globally significant freshwater biodiversity in the Mekong Basin ecosystem.