In the absence of reliable data on the species composition of the catch in the Lower Mekong Basin, the authors look at three approaches to estimate the size of the region’s migratory fish resources.The article, based on three different studies, concludes that 700,000 tonnes to 1.6 million tonnes of migratory fish are at risk. These possible losses correspond to respectively five times the size of the fishery sector in Finland and the whole fishery sector in Denmark.