Abstract
Background:
In recent years, parasitic helminths and their fish hosts have been used as a biomonitoring tool to indicate the status of ecosystems and their relationship with human health.

Aim:
This work aims to evaluate and use the potential ability of the cestode Schyzocotyle acheilognathi (Yamaguti, 1934) as a bioaccumulative indicator of zinc and iron, and compare it with the tissues of its final host, Common carp Cyprinus carpio Linnaeus, 1758, and to see if this cestode provides substantial evidence of the aquatic ecosystem pollution.

Methods:
Twenty-eight live fish were caught from the Tigris River passing through Rashidiya and Sharikhan sites in Mosul city, Iraq, during March 2024. The concentrations of Zn and Fe in the cestode tissues, gills, liver, intestines, and muscles of infected and uninfected fish were determined using an atomic absorption spectrometer.

Results:
The results showed that the ratio of accumulation of Fe and Zn in the cestode tissues to their host tissues was 1:0.622 and 1:0.616, respectively. In both uninfected and infected fish, the Zn levels were in the following order: gills > liver > intestine > muscles, while Fe levels were in the order liver > gills > intestine > muscles. Although the Fe concentrations were higher than the Zn in all samples that were analyzed, the values of Average Pollution Load Index were < 1, and they were within the permissible limits according to Food and Agriculture Organization and WHO.

Conclusion:
The cestode S. acheilognathi shows enormous promise as a sensitive bioindicator for heavy metal pollution in aquatic habitats, as does its fish host, Common carp C. carpio. Frequent observation of these species can yield early indicators in environmental monitoring programs.

Key words: APLI; Cyprinus carpio; Fe; Fish parasite; Zn.