Jorge Casciotta, Adriana Almirón, Lubomir Piálek and Oldřich Říčan
Abstract. The Gymnogeophagus setequedas group is based on our results composed of three endemic species of which one, G. taroba sp. n., is described as a new species. The three species are diagnosable from each other and from other species of Gymnogeophagus by stable differences in several morphological characters among which the best are found in coloration patterns. Body and head shapes and meristic characters show lesser differentiation but several are also clearly diagnostic in the G. setequedas group. The G. setequedas group is strongly structured allopatrically. The prime candidates for this fragmentation and speciation are the origins of the waterfalls on the individual tributaries. The largest of the waterfalls, the famous Cataratas del Iguazú, with a height of 72 m, separate G. taroba sp. n. from its closest relatives G. che and G. setequedas. The original 28 m high Urugua-í falls separate G. che from G. setequedas. Gymnogeophagus setequedas is separated from G. che and G. taroba by large rapids (about 65m in total elevation above the río Paraná) and a former fall on the Acaray river and by the 45 m high Monday falls located a few km from the mouth of the Monday into the río Paraná just opposite the mouth of the Iguazú.