The purpose of this application, under Article 75.6 of the Code, is to conserve the usage of the specific name of Macrobrachium rosenbergii (De Man, 1879) for a commercially important giant freshwater prawn from Southeast Asia by designating a neotype. Recent taxonomic reappraisals show that the two subspecies of this prawn, Macrobrachium rosenbergii rosenbergii (De Man, 1879) and M. rosenbergii dacqueti (Sunier, 1925) are in fact distinct species. The usage of the name M. rosenbergii for the species of prawn that is predominantly fished, cultured and studied by biologists is threatened, as its recently designated lectotype is M. dacqueti, while the holotype of M. rosenbergii is a different species, which has generated much less commercial and scientific interest. As substantial confusion will result if the names are changed, it is proposed that the existing holotype of Macrobrachium rosenbergii (De Man, 1879) be set aside and the lectotype of M. dacqueti (Sunier, 1925) be designated as neotype of Macrobrachium rosenbergii in its place. This action will allow biologists to retain the name M. rosenbergii for the commercially valuable species and will result in the less frequently used name M. dacqueti becoming a junior objective synonym of M. rosenbergii. For the species defined by the current holotype of M. rosenbergii, a new name Macrobrachium wallacei is proposed and a holotype is designated.