# Morphological and molecular assessment of muscle metacercariae infecting tench Tinca tinca from fish farms and wild populations in Germany

## TL;DR

This study identifies zoonotic parasites in farmed and wild tench in Germany, highlighting a risk to human health if the fish is consumed undercooked.

## Contribution

The study combines morphological and molecular methods to identify specific zoonotic trematodes in tench for the first time in Germany.

## Key findings

- Three trematode species were identified in tench muscle tissue, including two with zoonotic potential.
- Pseudamphistomum truncatum and Paracoenogonimus ovatus showed high prevalence in both farmed and wild tench.
- Accurate identification of metacercariae is critical for assessing food safety risks in fish consumption.

## Abstract

Fish can be infected with metacercariae (the final larval stage) of different species of potentially zoonotic digenetic trematodes (flukes). The fish-borne zoonotic trematodes thus compromise food safety and present a major threat for human health. Reducing the risk of human infections requires careful assessment and accurate taxonomic identification of these parasites. Here, we analysed metacercariae in muscle tissue of tench (Tinca tinca), sampled between March and September 2022 from three fish farms and three natural waterbodies in Germany. Whenever possible, we combined morphological and molecular data from the very same individual metacercariae using mitochondrial cytochrome oxidase c subunit 1 (cox1) and nuclear internal transcribed spacer 1 (ITS1) for species identification. Three morphotypes of metacercariae were found in the muscle of tench, corresponding to the trematode species Pseudamphistomum truncatum Rudolphi, 1819 (Opisthorchiidae), Hysteromorpha triloba Rudolphi, 1819 (Diplostomidae), and Paracoenogonimus ovatus Katsurada, 1914 (Cyathocotylidae). The high prevalence of metacercariae of P. truncatum and P. ovatus, both with zoonotic potential, poses a risk for human infections if undercooked or raw tench is consumed.

The online version contains supplementary material available at 10.1038/s41598-025-09396-y.