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In the present study, Labeo rohita were exposed to carbosulfan for 96 h. Experimental fishes which measured an average length of 6±7 cm and weighed 6.5±7.5g. Nine groups with three replicates of experimental fish were exposed to seven concentrations of carbosulfan. The containers used for the test media of 15 L capacity, filled with dechlorinated water. Where maximum 10 fishes were used in our experiments for each concentration, 10 fishes were also maintained in separate container along with experimental groups, served as control. The median lethal concentrations (LC50) of carbosulfan for 96 h were 1.2mg/l, respectively. In addition, to dose and dose-time dependent increase in mortality rate, the behavioral changes of L. rohita at different concentrations of carbosulfan were determined. Physiological responses like rapid opercular movement, hyper secretion of mucus and frequent gulping of air was observed during the initial stages of exposure after which it became occasional. The unusual behaviour of the fish L. rohita in stress condition may be due to obstructed functions of neurotransmitters. All these observations can be considered to monitor the quality of aquatic ecosystem and severity of pollution. In conclusion, carbosulfan was moderately toxic to freshwater fish L. rohita.