Occurrence and molecular identification of Paracoenogonimus ovatus and Holostephanus dubinini, with a tentative detection of Diplostomum spathaceum, in commercial fish

Ainur A. Zhaksylykova, Zaure Z. Sayakova, Saltanat A. Kenessary, A.A. Abdibayeva

German Journal of Veterinary Research, 2026

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DOI 10.51585/gjvr.2026.3.0205
Data confidence 70 medium
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Abstract

This study presents the first data on the prevalence, host range, geographic distribution, and molecular characterization of digenean trematodes infecting the muscle tissue of commercially important freshwater fish in Kazakhstan.A total of 1,209 fish specimens, representing 29 species from 19 water bodies across seven major fishery basins, were examined.Parasitological assessment was conducted using compression microscopy, and species identity of metacercariae was confirmed through molecular analysis with ITS1 and cox1 markers.Metacercariae were detected in 16 fish, resulting in an overall prevalence of 1.32%, with infection intensities ranging from 1 to 73 metacercariae per infected fish.Paracoenogonimus ovatus metacercariae were identified in six fish species (prevalence 1.16%) from the Nura-Sarysu and Zhaiyk-Caspian basins.Holostephanus dubinini metacercariae were detected in a single common rudd (Scardinius erythrophthalmus) from the Kigash River and a single ide (Leuciscus idus) from the Nura River.P. ovatus and H. dubinini were identified to species level using ITS1 sequences and phylogenetic analysis.The cox1 data supported the ITS1-based identification of P. ovatus but did not independently confirm species identity.Additionally, one bream (Abramis brama) specimen from the Zhaiyk River yielded a mixed-template result: ITS1 identified P. ovatus, while the cox1 marker tentatively detected DNA from Diplostomum spathaceum.This finding is preliminary and requires independent verification.The study also reports the first GenBank submissions from Kazakhstan of the ITS1 and cox1 nucleotide sequences of P. ovatus, the ITS1 sequence of H. dubinini, and a cox1 sequence tentatively attributed to D. spathaceum.The limited distribution of P. ovatus, and particularly H. dubinini, suggests that local transmission depends on the presence of suitable first intermediate gastropod hosts.The ecological requirements of these hosts may restrict these trematodes to specific water bodies.The findings expand current knowledge of the distribution of digenean trematodes in commercially important freshwater fish of Kazakhstan, provide new insights into their molecular diversity, and provide a basis for further epizootiological monitoring and assessment of potential parasitological risks.