ABSTRACT Background: The Present study was carried out to track and calculate Biomagnification Factor (BMF) of total mercury (T-Hg) between two different trophic levels (i.e., plankton and a planktivorous fish) in a fresh water grazing food chain. Methods: Experimental organisms were planktonic biomass and silver carp (Hypophthalmichthys molitrix) as a planktivorous fish. Silver carp samples were obtained from randomly selected points from different sampling stations. The concentrations of T-Hg in collected samples were determined by Advanced Mercury Analyzer. Results: Means of T-Hg in planktonic biomass and muscle tissue of silver carp were 78.21 ± 3.13 and 367.12 ± 26.43 ng g-1 dry weights, respectively. Mean T-Hg in plankton, sampled fish during the study months and amongst the sampling stations did not show significant differences. The BMFHg(plankton-fish) was differ among months; moreover, calculated BMF was greater than 1 during study months, which means biomagnification was occurring in SGR. The concentration of T-Hg in the muscle tissue of all fish samples that weighed more than 850 gr was higher than the acceptable limits based on EPA (300 ng g-1) and WHO (500 ng g-1) standards. The highest BMFHg was observed in August Conclusion: It seems that mercury pollution of SGR has a natural source. The calculated BMFs were greater than 1 and the concentrations of T-Hg in muscle tissues of those samples weighing more than 850 gr were higher than FAO and WHO standards. Therefore, consumption of the SGR's silver carp must be accompanied by serious health considerations. Keywords: Biomagnification, Grazing Food Chain, Mercury, Plankton, Silver Carp.
