"Felipe asked me to give my impression on Uruguayan fishes based on recent field expeditions to that country and I few comfortable in doing that. Uruguay and Rio Grande do Sul state of Brazil are pretty similar in their faunal compositions and at the same time so diverse that we can talk about the whole region to give a better idea about the fish diversity to be found, as well as the differentiated patterns of distribution of these fishes (when we look an Atlas of South America it gives us the impression the rio Uruguay is holding Uruguay and Rio Grande do Sul together and separate form the rest of South America).

Two larger freshwater drainages almost half split the region: the rio Uruguay to the West and the lagoa Mirim - laguna dos Patos to the East. Although very close located geographically, both drainages present considerably different faunal compositions. The number of described species to the rio Uruguay drainage can be roughly estimated as near 175 species and to the lagoa Mirim - laguna dos Patos drainage as about 125 described species. The impressive, however, is the fact that only approximately a third part of these fishes (75 species) are common to the two drainages. That means when we travel East-West we find different species of fishes in a few kilometers distance. It is just necessary to cross water divisors between those drainages. The rio Negro, crossing the center of Uruguay and although a tributary of the rio de La Plata just like the rio Uruguay, also presents some peculiar species.

Species diversity in the region is not only determined by the drainages. We also find differences inside drainages. Part of this diversity is associated with the different biotopes found along the country. The rocky bottom environments to the northwest, near Artigas, for example, present peculiar cichlid species not found in the remaining portion of the country. The same occurs in the fine grain sand bottom of some portions of the rio Negro, as well as when we collect in swamp environments or even in larger rivers.

Some of the most beautiful species are those of the genus Gymnogeophagus, whose males develop extremely beautiful color patterns during reproductive periods. However, the most interesting point regarding cichlids in Uruguay (and similar to what we observe in Rio Grande do Sul, Brazil) is the diversity of species we find collecting in different streams of the same river as well as in streams from different drainages."