First record of Cyprinion macrostomum (Cyprinidae) outside its natural range in Türkiye and limitations of COI barcoding in species identification based on S7 gene evidence

Abstract

Cyprinion macrostomum Heckel, 1843 is a species of Cyprinidae whose natural distribution in Türkiye is limited to the Euphrates-Tigris river system. This study presents the first record of C. macrostomum outside its natural range, from a hypothermal spring in Western Anatolia (Pınarbaşı Spring, Tefenni-Burdur). Species identification was clearly made based on morphological characters; however, molecular verification using mitochondrial COI barcode gene analysis failed to differentiate C. macrostomum from its closely related congener C. kais. The 100% sequence similarity between the two species revealed that the COI gene region has limited discriminatory power for distinguishing these closely related Cyprinion species. In contrast, maximum likelihood (ML) phylogenetic analyses based on the nuclear S7 ribosomal protein gene recovered the two species as clearly distinct lineages. The findings suggest that the COI barcode gene alone may be insufficient for resolving species boundaries among some closely related Cyprinion taxa, whereas the S7 gene is a more reliable molecular marker. Monitoring of this extra-regional population is recommended to evaluate its persistence and ecological interactions within the study area.