Rheocles vatosoa, sp. nov., an endemic Madagascan rainbowfish, is described from the Lokoho River basin in the region of Andapa in northeastern Madagascar. Rheocles vatosoa has the northernmost distribution of the genus recorded to date. The species differs from congeners in the possession of a single (versus three) interdorsal pterygiophore and is additionally readily distinguished from the other two “northern species”; R. pellegrini, from a locality “one day west of Andapa”, and R. derhami from the Ambomboa River (Sofia drainage), by the possession of a fully scaled dorsum, nape, and venter.