Arapaima are listed as endangered fishes according to the Convention on International Trade of Endangered Species of Wild Fauna and Flora (CITES), thus their international trade is regulated by non-detriment finding (NDF) procedures. The authors critically assessed Brazil’s regulations for NDF procedures for Arapaima using IUCN’s checklist for making NDFs, and found that those regulations cannot ensure the sustainability of Arapaima populations. Arapaima are among the largest fishes in the world, migrate short distances among several floodplain habitats, and are very vulnerable to fishing during spawning. They are threatened mainly by overfishing. The fishery is largely unregulated because government regulations on size, season, and even moratoriums on capture have been very poorly enforced. Arapaima remain poorly understood and the taxonomy and geographical distribution of the genus remain uncertain. There are no data on catch levels or status of wild populations, although available information suggests they are in decline. Brazil’s NDF procedures for specimens originating in the wild are inadequate as they rely on ‘technical opinion reports’, which do not necessarily require scientific evidence. Furthermore, Brazil’s NDF procedures exempt the need for NDF reports on ‘captive’ specimens; however, ‘captive’ specimens originating in the wild and raised in captivity can be exported because regulations do not specify that they must be ‘captive-bred’. Six suggestions are offered to improve the reliability of NDF procedures for Arapaima in Brazil, emphasizing the utility of participatory monitoring and adaptive harvesting to strengthen much needed harvest control capacity in other tropical fisheries.