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The mercury content in 158 fishes and 28 mussels in the Second Songhua river were detected. The range of mercury concentrations in fishes and mussels was 0.02-0.66 mg/kg and 0.002-0.056 mg/kg, respectively. The history change of mercury content in fishes was analyzed in this paper. From upstream to downstream, the average mercury concentrations in fishes increased with the increase of the distance to the headstream, then decreased in the downstream of Wujiazhan town (sampling site). The fact illuminated that the source of mercury contamination was mercury in sediment. In the different species of fishes, the mercury concentration in Parasiburus asvtus was the highest and the order of mercury distribution in fishes was: the mercury value in fishes in the river bottom >that in fishes in the surface and that in predacious fishes>that in herbivorous fishes. In the investigation, there were amount of fishes whose mercury value exceeded the criterion for that in fishes that suggested that the mercury contamination in the Second Songhua River have not completely been eliminated until now.