Abstract
Background:
Pollution of aquatic environments with heavy metals cause severe adverse effects on fish, invertebrates and human. The importance of this study lies in the fact that long-term ingestion of heavy metal-contaminated fish can result in the accumulation of harmful metals in numerous organs and pose a major risk to human health.

Aim:
Current study was designed to investigate the concentrations of toxic arsenic (As), lead (Pb) and mercury (Hg) in the liver, gills and muscles of highly consumed aqua cultured common carp (Cyprinus carpio L.) in Baqubah city, to evaluate the toxicopathological bioaccumulation of As, Pb and Hg in consumed fish and the potential human health risk after consumption and give clear indication for a status of heavy metal contamination for water used in aquaculture of common carp (cyprinus carpio L.).

Methods:
A total of ten Fresh fish of common carp (Cyprinus carpio L.) were randomly selected from local Baqubah markets / Diyala province/ Iraq in different interval from September 2022 to January 2023. The source of fish in Baqubah’s local markets is fish aquacultured in earthen ponds as well as cages in the Tigris River in Diyala province. Flame atomic absorption spectrometer (FAAS) was used to estimate the level of As, Pb and Hg in liver, gills and muscles of collected fish. Histopathological sections were prepared for evaluation of toxic pathological effects of metals on Cyprinus carpio organs.

Results:
Bioaccumulation of arsenic and lead in liver, gill and muscle samples was within and less than the permissible limit set by WHO while the bioaccumulation of mercury exceeds the permissible limits set by WHO. Histopathological findings of gill section showed telangictatisis and epithelial lifting in secondary lamellae with hemorrhage and blood congestion and central venous dilation and epithelium hyperplasia with complete fusion of the secondary lamellae and edema in the filamentary epithelium in addition to mononuclear cells infiltration. Histopathological findings of liver revealed degenerative and necrotic changes in liver tissue distinguished by pyknosis with existence of necrosis in cells and dilation of the sinusoids with cytoplasmic vacuolation.

Conclusion:
The bioaccumulation of mercury is higher than permitted levels in common carp (Cyprinus carpio) which indicate high contamination level of main sources for fresh waters in Diyala province mainly from Diyala and Tigris rivers.

Key words: Bioaccumulation, Heavy metals, Cyprinus carpio, Human health, Pathological effects