DNA barcoding of invasive Gambusia holbrooki Girard, 1859 and Atherina boyeri Risso, 1810 inhabiting Upper Euphrates River Basin, Türkiye.

The main contributor to Türkiye's abundant freshwater fish biodiversity is its geographic location. This fauna consists of endemic, native, and non-native fish species. The introduction of Gambusia holbrooki Girard, 1859 to Lake Amik in the 1920s for the biological control of malaria was the first introduction of nonnative species to Türkiye. Atherina boyeri Risso, 1810 and other nonnative fish species have recently been introduced to Türkiye's freshwaters. In this research, the first records of invasive Gambusia holbrooki (Keban Dam Lake, in Elazığ Province) and Atherina boyeri (Karakaya Dam Lake, in Elazığ Province) are cited from the Upper Euphrates River Basin in the Eastern Anatolia Region of Türkiye. In situ electrofishing equipment was used to gather the specimens. Fish muscle samples were used to extract genomic DNA, which was then used to barcode the mitochondrial cytochrome c oxidase subunit I (COI) gene to identify different species of fish. The identification of invasive fish species using DNA barcoding is an effective technique, as evidenced by the comparison of amplified COI sequences to the BLAST database.