Abstract

Freshwater ecosystems are increasingly exposed to metal contamination arising from natural and anthropogenic activities, potentially affecting fish physiology and ecosystem health. However, limited information is available regarding metal accumulation and associated biological responses in fish populations from Dukan Lake, northern Iraq. Therefore, this study investigated metal concentrations in water and tissues of common carp (Cyprinus carpio) and evaluated their relationships with selected fish health indicators. Water and fish samples were collected monthly from Dukan Lake, and a total of 60 fish were classified into three length groups (20–29 cm, 30–39 cm, and 40–49 cm). Metal concentrations in water, liver, and gonad tissues were analyzed using ICP-OES, while condition factor (CF), gonadosomatic index (GSI), and hepatosomatic index (HSI) were used to assess fish physiological condition. Sodium (Na), magnesium (Mg), potassium (K), iron (Fe), zinc (Zn), and barium (Ba) were detected in both water and fish tissues, with concentrations in water ranging from 50 to 7069 μg/L. In contrast, chromium (Cr), manganese (Mn), nickel (Ni), selenium (Se), silver (Ag), cadmium (Cd), antimony (Sb), lead (Pb), copper (Cu), and arsenic (As) were below detection limits. Biometric analysis revealed significant differences (p < 0.05) in the gonadosomatic index (GSI) among fish length groups, indicating size-dependent reproductive development. However, no significant relationship was observed between fish length and either the CF or HSI, suggesting relatively stable somatic condition or liver status across size classes. Correlation analysis showed no significant associations between water metal concentrations and CF or GSI. A significant positive correlation was identified between Zn concentration and HSI in the 30–39 cm length group, indicating a possible link between Zn exposure and hepatic physiological response. The findings indicate that essential elements dominate the metal profile in Dukan Lake, with limited evidence of toxic metal contamination. No major adverse effects on the general condition of the fish were observed. These results contribute to understanding metal bioaccumulation patterns and their implications for fish health in freshwater ecosystems.

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