Determination of LC50 of Copper Sulfate and Lead(II) Nitrate and Behavioral Responses of Grass Carp (Ctenopharyngodon idella)

In the present study, grass carp (Ctenopharyngodon idella) were exposed to copper and lead for 24, 48, 72 and 96 h. Experimental fishes which measured an average length of 8.2 ± 0.44 cm and weighed 4.3 ± 0.5 g. Seven groups (with three replicates) of experimental fish were exposed to seven concentrations of each metal. The grass carps were kept in 21 tanks each stocked with 30 fishes were used in our experiments for each metal. The median lethal concentration (LC50) of copper to grass carp for 24, 48, 72 and 96 h were 2.422 mg/L, 2.222 mg/L, 2.006 mg/L, and 1.717 mg/L respectively. The median lethal concentration (LC50) of lead to grass carp for 24, 48, 72 and 96 h were 293.747 mg/L, 278.019 mg/L, 260.324 mg/L, and 246.455 mg/L, respectively. In addition, the behavioral changes of grass carp at different metal concentrations were determined. LC50 increased as mean exposure times decreased for both metals. Physiological responses like rapid opercular movement and frequent gulping of air was observed during the initial stages of exposure after which it became occasional. All these observations can be considered to monitor the quality of aquatic ecosystem and severity of pollution. In conclusion, copper is more toxic than lead for grass carp.