Acute toxicity bioassay of mercury and silver on Capoeta fusca (black fish).

Since toxicity is based on the effect that a toxicant produces at a target site within an organism, establishing the relationship between the concentration of substance at the target site and the subsequent toxic effect can provide a tool for predicting toxicity. The behavior of a single toxicant could not be fully understood without the knowledge of the fact the physical and biochemical properties of substances that can change. To understand this, the acute toxicity of mercury (as HgSO₄) and silver (as AgSO₄) to Capoeta fusca (6 treatments in triplicate) was determined. During September 2009, C. fusca belonging to the family Cyprinidae, weighing 2.95 (±0.55) g, were obtained from qanats in Birjand, East of Iran. The fish were maintained in an aquarium system at a holding temperature of 21 (±0.2) and were allowed to adjust to lab conditions for 1 week before experimentation. The lethal concentration 50 (LC₅₀) values for HgSO₄ at 24, 48, 72, and 96 h of exposure were 0.32, 0.28, 0.26, and 0.24 mg L⁻¹, respectively. Also, the LC₅₀ values for AgSO₄ at 24, 48, 72, and 96 h of exposure were 0.014, 0.013, 0.013, and 0.013 mg L⁻¹, respectively. Results of this study showed that C. fusca was very sensitive to AgSO₄.