Determination of distribution ranges of garra hamilton, 1822 species inhabit the upper tigris-euphrates river system

In this thesis, the critical diagnostic characters of 1658 individuals belonging to 3 Garra species, inhabit Turkish part of the Tigris-Euphrates river system, and deposited in two large fish collections within 96 lots, were analysed and their current distribution ranges were examined. The applicability of the examined diagnostic characters in taxonomy and the accuracy of the range values of these characters were examined. The main subject of the study was G. rufa and G. rezai rather than G. variabilis, since it is the most easily distinguished morphologically from the other two species. Garra rezai was recently described from two geographically distant areas in the Tigris drainage: upper Yanarsu River (eastern Türkiye) and Bouein-Sofla Creek (Iran). After the description of G. rezai, there was a need to reveal the interesting situation in the distribution range of this species. Therefore, it was aimed to determine the distribution ranges of morphologically closest G. rezai and G. rufa in Türkiye by analysing specimens collected between 1957 and 2023 in two large fish collections. To achieve this, we focused on the most important morphologically diagnostic characters that distinguish these two species: scales on predorsal midline between dorsal-fin origin and nape, and branched dorsal-fin rays. The results revealed that G. rufa remains a widely distributed species in the Tigris-Euphrates catchment, while G. rezai is regionally widespread, with populations identified in at least six different regions within the Tigris catchment. Additionally, G. rezai was documented for the first time in the upper Euphrates. Furthermore, we identified the streams where G. rezai coexists with G. rufa.