MT-CO1 and infection: Specifically, the objectives were to (i) conduct monitoring surveys of cyprinid fish from three lakes in the Akmola region to determine the prevalence and intensity of infection with Opisthorchiidae metacercariae, (ii) perform morphological identification of O. felineus and M. bilis larvae, (iii) develop and apply a multiplex PCR assay targeting the mitochondrial cytochrome c oxidase subunit 1 (COX1) gene to achieve species-level differentiation, and (iv) validate molecular identification through sequencing and phylogenetic analysis.