Water pollution by metals and subsequent fish contamination are considered to be severe problems with detrimental ecological consequences. The purpose of the present study was to determine the median acute toxicity (LC 50) of copper (Cu) and cadmium (Cd) in kutum, Rutilus frisii kutum fingerlings. Also, using sub-lethal tests, metal accumulation and gill ion changes were evaluated. Fingerlings (1.1 ± 0.25 g) were exposed to different concentrations of CuSO 4 ·5H 2 O and CdCl 2 .2·5H 2 O in the static bioassay OECD test. In definitive tests, fish were exposed to nominal concentrations of 0.127, 0.229, 0.330, 0.432, 0.534, and 0.636 mg/l of Cu and 3.938, 6.893, 9.847, 12.801, 15.755, and 18.709 mg/l of Cd. Results from a Probit analysis showed that 96-h LC 50 values were 0.45 and 12.22 mg/l for Cu and Cd, respectively. Semi-static sub-lethal tests were conducted with nominal concentrations of 0, 12.7, 25.4, 50.9, and 101.8 μg/l of Cu and 0, 0.1, 0.25, 0.5, and 1 mg/l of Cd for 4 days. Significant accumulations were observed in gill Cu/Cd levels in all treatments in comparison to the controls (P < 0.05) with a maximum average of 22.32 ± 1.25 μg Cu/g gill wet weight at 12.7 μg Cu/l treatment and 6.18 ± 0.44 μg Cd/g gill wet weight at 1.0 mg Cd/l treatment. Finally, no significant (P > 0.05) changes were observed in gill sodium and calcium contents during Cu/Cd exposure. In conclusion, Cu is more toxic than Cd for kutum, and it has higher uptake in the gills

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