Non-native species have long plagued aquatic environments and are considered major global threats to native biodiversity. This problem is especially pertinent in large tropical river systems, but information on their prevalence and distribution is typically limited. This study examines the diversity, distribution, and contribution of non-native fish species to the fisheries and biodiversity of the Mekong basin and potential actions to manage adverse impacts on native fish fauna. The assessment is largely based on reviewing existing literature, information, and data, supplemented by fisheries catch and aquaculture production data for the region. One hundred and seven non-native fish species, distributed amongst 36 Families and 14 Orders, have been reported in the Mekong basin. This count represents ∼7.3% of the overall fish species diversity. Where known, the majority of fish species were introduced for aquaculture or ornamental purposes. The greatest contributions of non-native species to total catch were in upper Lao PDR and the Mekong Delta. These zones coincide with areas of intense aquaculture production, especially cage culture along the riverbanks. There is a divergence of species cultured in different countries, with production dominated by non-native species, especially Oreochromis niloticus, in Thailand and Lao PDR, but native species in Vietnam and Cambodia. Given the proliferation of non-native species in the Mekong, there is an urgent need for action to avoid deterioration of the native fish fauna. It is recommended that continuous monitoring is carried out on the distribution and spread of non-native species in the Mekong, including introduction and invasion pathways, to focus regional management measures to remediate any pending threats to biodiversity and fisheries.

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